Shōgun, FX’s period drama-action series on Hulu, has drawn comparisons to Game of Thrones, thanks to its shocking violence, like people pulling out their own guts with swords and others being boiled alive slowly. Unlike that brutal flight of fantasy, however, Shōgun is based on the 1975 historical novel of the same name by James Clavell — which was inspired by true events during the late Sengoku period (1467–1615) in Japan. In other words, there’s something real to this horror. This time was ripe to be fictionalized, defined by civil wars among different liege lords across the land — called daiymō — and social upheaval. In the show and book, John Blackthorne (Cosmo Jarvis), a rough-mannered English sailor, washes up on the shores of a Japanese fishing village and finds himself helping the frightening and strategic Lord Yoshii Toranaga (Hiroyuki Sanada), who aims to win control of Japan, end the infighting, and become shōgun, a military dictator. While the events are dramatic, the history the show is anchored in is quite real.

Blackthorne is based on William Adams, the first Englishman to reach Japan, and Toranaga is based on Tokugawa Ieyasu, whose shogunate ushered in the Tokugawa period, which is known as a time of economic growth and internal stability after generations of feuding samurai clans. Toda Mariko (Anna Sawai), a powerful and graceful Christian Japanese noblewoman who is Blackthorne’s translator (and love interest), is inspired by the very real Hosokawa Gracia, who served a critical role in Tokugawa’s war.

In the show, Mariko is somewhat loyal to the Catholic Portuguese missionaries who converted her (although ultimately she gives near-total obedience to her liege lord, Toranaga). Blackthorne, a Protestant, worries that Mariko’s loyalties to the Portuguese will interfere with their budding romantic connection, not to mention his reliance on her as one of the few people in Japan who serve as his translator. In an attempt to make his Japanese captors/hosts distrust his Catholic Portuguese rivals, Blackthorne dramatically reveals to Toranaga and Mariko that the Portuguese aim to colonize Japan, and that they already have colonies in Macau, shocking the Japanese nobility.

This is a piece of colonial history in East Asia we rarely see in the mainstream media, so let’s unpack it. What’s the real story of Portuguese presence in Japan?

Did the Portuguese try to colonize Japan?

Yes. Because of the fierceness of the warrior class and Japan’s distance from Europe, the Portuguese didn’t have the ability to conquer Japan through force, the way they did in places like Brazil and parts of India. Instead, they used religious conversion and trade to try to accomplish a cultural and economic conversion, exploiting the fractious nature of the warring lords to expand their trade routes. In fact, Japan still bears marks of Portuguese contact. As Morgan Pitelka, professor at UNC Chapel Hill and expert on late medieval and early modern Japan, notes some Japanese food dishes have names derived from Portuguese, like pan for bread, karumeira for caramel, and hasuteira for pie crust. Other sources even attribute the name and recipe for the Japanese dish tempura to the Portuguese, although Pitelka says that is up for debate.

Some might think that the lack of military force means there was no attempt at colonization, but it’s important to understand that conquering a society doesn’t always require armies. “If you think about conversion as a colonizing mission, it means someone is saying ‘Your religion is wrong, come over to our religion,” says Nicole Freiner, associate professor of Political Science at Bryant University and author of The Social and Gender Politics of Confucian Nationalism: Women and the Japanese Nation-State. “The records say that the Portuguese probably converted thousands of Japanese. Even though the Tokugawa shōguns tried to eliminate all Christianity, it did persist.” So, yes the Portuguese did try to colonize Japan. They just weren’t successful, ultimately. And we’ll get to why they weren’t successful later.

Did the Portuguese enslave Japanese people?

The show has not yet made mention of this history, but it did happen. To get more clarity, we spoke to Liam Brockey, professor of Early Modern Europe and historical consultant on the 2016 Martin Scorsese film Silence, which is about two 17th-century Portuguese Jesuit priests who travel from the Portuguese colony in Macau to Japan to find a missing missionary and spread Christianity in Japan. Brockey says that there are “concrete references to Portuguese buying slaves in Japan.” The Portuguese also captured and paid for enslaved people from China and Korea. According to Pitelka, many of those enslaved people ended up in Macau, now an autonomous region on the south coast of China. In the show, when Blackthorne plays the hero and informs Lord Toranaga and Mariko that the Portuguese have a colony there, the Japanese nobility are shocked. But in reality, this was not only common knowledge but was actually encouraged by Japan’s rulers who saw the Portuguese as beneficial to their economy — for a time, anyway.

Brockey says enslaved Japanese sometimes ended up as far away as Portuguese colonies in India, such as Goa and Cochin, or they were moved and sold again elsewhere in East Asia. Brockey says this was a “vibrant slave trade,” but with a few differences from the trans-Atlantic slave trade of West and Central Africans. “There was an understanding in Japan and China that you could make enough money at some point to repurchase your freedom.” However, he stresses it was not indentured servitude, but slavery.

Did the Portuguese and British fight over Japan?

It is this backdrop of attempted colonization that forms much of Blackthorne’s journey as an Englishman in Japan. The show opens by saying, “For decades, Portuguese Catholics have richly profited from trade in Japan. They have kept its whereabouts hidden from their sworn enemies — the European Protestants.” While Adams’s letters to his English wife back up that they were in search of the “East Indies,” it’s not true that the location was completely hidden. Brockey says that maps printed by Dutch cartographers in the late 1500s clearly showed where Japan was. “Where Japan laid was no secret. But how to get there, and how to get past all of the fortifications that the Portuguese built between Europe and East Asia, was a totally different challenge,” he said.

Letters from Adams to his English wife — Adams stayed in Japan for the rest of his life and started a Japanese family — show that he considered landing there to be a great achievement and the ambitious daiymō Iyeasu to be a prized ally. “I showed unto [Tokugawa Ieyasu] the name of our country, and that our land long sought out the East Indies, and desired friendship with all kings and potentates in way of merchandise, having in our land diverse commodities which these lands had not,” Adams wrote to his wife.

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According to Pitelka, the portrayal of Blackthorne’s extreme animosity toward the Portuguese sailors and missionaries and his race to make himself and the Protestants the center of trade there reflects the times, when conflict between Catholics and Protestants engulfed Europe after Martin Luther’s Reformation movement began in in 1517.

Pitelka says these conflicts were not just about religion. They were about money. “This is the moment when capitalism is beginning. The corporations that are formed through these explorations of the world — the Dutch East India Company and British East India Company — are the first capitalist corporations, and they are partially sponsored by their governments,” he tells Vox.

However, the show implies through Blackthorne’s accusations and warnings to Toranaga that the British and Dutch alliance have more innocent aims in Japan, which isn’t true. The British didn’t have good intentions for East Asia, but they were more focused on conquering land and trade routes in South and Southeast Asia. “Their goal was to extract resources from the rest of the world to conquer to create colonies so that they could keep fighting in Europe. It’s the dysfunction in Europe, the fact that they’re all constantly waging war with each other that drives this colonial expansion around the world,” Pitelka explains. “The Spanish and the Portuguese are in Asia because they want to either enslave people or find gold and silver, or take spices and porcelain and silk back to Europe and sell it to beat their rivals. The English and the Dutch are exactly the same way.”

And Pitelka confirms that this colonization was happening in multiple arenas — through trade domination, religious conversion, and military conquest/expansion. “[Blackthorne’s] animosity toward the Portuguese and the Spanish and their animosity towards him is one of the most accurate parts of the show,” he says. And in the end, Adams got his way. “He encouraged the Dutch to send trading ships to Japan and they were eventually able to do so in 1609,” Pitelka says, adding that for the rest of the Tokugawa period, the Dutch Protestants replaced the Portuguese Catholics as the primary European trading partners in Japan. After the Shimabara Rebellion — an uprising of Japanese Catholics — in the late 1630s, the non-Christian Japanese rulers set limits their to Christian power, and the Portuguese were banned from trading in Japan.

Was seppuku common?

One historical practice raising eyebrows and questions in Shōgun is seppuku — a Japanese form of ritual suicide by disembowelment, which plays a huge role in shaping the story. In the first episode, one of Toranaga’s vassals speaks out of turn at a meeting, causing conflict. His solution when he realizes his mistake is to immediately offer to kill himself and his infant son, ending his family’s line. He and the other vassals are even annoyed at his wife, Fuji (Moeka Hoshi), for protesting her son’s murder; she, in turn, never expresses any anger at her husband or her liege lord for their responsibility in his death.

But was seppuku really this brutal or common as the show makes it seem? And did those who were commanded to perform it or watch their family members perform it put up so little dissent?

Pitelka says that we shouldn’t think of it as commonplace, but rare due to the exclusivity of the samurai class, who were military nobility. “In this period, the samurai are probably less than 6 or 7 percent of the population. And only the most elite of the samurai were obsessed by issues of honor and status to the degree that they would pursue seppuku.” However, he says that among this small group, seppuku was a real practice that happened the way it’s depicted in both Clavell’s book and the show. “There’s a famous example from the life of Tokugawa Ieyasu,” he says, “who’s the real warlord Toranaga is based on, where his son did something to disgrace him and he ordered his son, and his son’s mother — who was his wife — to kill themselves.”

As far as willingness to kill yourself whenever a lord told you to, Pitelka says seppuku was preferable, because by the time it was commanded, death was certain anyway. “The only alternative to seppuku was execution,” he says. “The idea is you have shamed yourself. Rather than being executed where your power over your life is taken away, they are respecting your position as a samurai and letting you take your own life, which in the samurai code of honor, is a better way to die than a firing squad.”

Pitelka says there wasn’t a lot of pushback because this was “a profoundly militaristic society,” without “any notion of individual liberties or freedom.” This matches the world Shōgun portrays, where Toranaga has absolute control, and we see minimal negotiation or rebellion.

Pitelka points out a torture scene from the beginning of the show, where an English soldier is slowly boiled alive until he dies. And when you put it that way, it makes sense why someone might choose seppuku.

Why did the Portuguese not ultimately succeed in colonizing Japan?

Well, the answer to that not only lies in how difficult it was to get to Japan from Europe, but also the military culture characterized by seppuku.

Pitelka stresses that the distance of Japan shielded it from much of the “cancerous European expansion and extraction” that other countries endured. “There was never a full naval invasion of Japan by Europeans. At most, they could send one ship with some priests and merchants per year. Some years they couldn’t do it at all because the ship sank, so the ship got stuck someplace.”

But it wasn’t just geography. Daiymō and the shōgun had absolute power over their people, and Japan was a military dictatorship where resistance meant death. Pitelka tells Vox that “the attempts to penetrate that did occur encountered fierce displays of strength and a very strong desire to protect Japan from outsiders.” While the show depicts the Japanese nobility as being shocked and then passive about Portuguese expansion, they actually began to grow deeply disturbed at the pressure to convert and the Portuguese accumulation of silver. “Japan was one of the main sources of silver in the world at this time. So they wanted to protect their economy as well,” Pitelka says. “And once the samurai started to learn that the European Catholic nations were invading and conquering other countries like the Philippines, they immediately realized this was dangerous and they had to isolate and control the Europeans.” It was the frightening violence, the control, and the military skill that Shōgun depicts that enabled the Japanese to do that.

Pitelka stresses, however, that we still shouldn’t glorify the samurai or shōguns, because they were military dictators who were very cruel to lower classes, and their legacy has often been used for more disturbing projects of Japanese nationalism, like the occupation of Korea from 1910 to 1945 or the current attempts to remilitarize its own society. It’s a sobering reminder that our history should never be used to justify going backward in the present. But it is rich material for one of the best new shows of the year.