I've seen posts and heard people talk about GoT being based on actual happenings, what are they?
Edit: that includes A Song of Ice and Fire.
Note: I'm focusing on ASOIAF, not the show.
Well, the whole thing has a significant fantasy-ized medieval European element. See here
Is it true that you based A Song of Ice and Fire off the War of Roses?
No, not really. Certainly I wanted to give my series a strong grounding in real medieval history, rather than in other fantasy novels, but I drew on a whole number of sources and periods. The Wars of the Roses, yes, but also the Hundred Years War, the Crusades, the Norman Conquest... you name it.
Most of my borrowings, however, come from English and French medieval history, simply because I am more familiar with those than with the heroes, legends, and traditions of other countries. The Wars of the Roses, the Crusades, and the Hundred Years War have been my biggest influences... oh, and some Scottish history as well, such as the infamous Black Dinner that inspired my own Red Wedding. This isn't a matter of choice so much as it is one of necessity. I don't have any other language besides English, and there's a paucity of good popular English language histories about medieval Spain, medieval Germany, and the like. I was in Germany last fall, and looked everywhere for good reference books about the medieval Holy Roman Empire, which would be treasure trove, I suspect. There are a ton of them that looked likely... but all in German.
The Wars of the Roses have always fascinated me, and certainly did influence A SONG OF ICE AND FIRE, but there's really no one-for-one character-for-character correspondence. I like to use history to flavor my fantasy, to add texture and versimillitude, but simply rewriting history with the names changed has no appeal for me. I prefer to reimagine it all, and take it in new and unexpected directions.
These three replies sum up most of what Martin himself has said on the issue.
EDIT: I wanted to add something about the Dothraki who are supposedly Mongol, since a lot of people make the connection.
The Dothraki are not the Mongols. Instead, they can be seen as GRRM's version of the trope of the cruel Asiatic steppe warrior, and are, generally speaking, wildly incompetent compared to the actual Mongols. Besides their apparent incapability of siege warfare, their, pardon my french, complete idiocy is highlighted in the Battle of Qohor; no real-life mounted cavalry army composed of real, breathing people would charge a shield wall with high casualties eighteen times without flanking it, when they are outnumbering the shield wall seven to one. They fulfill their literary trope well, but they fail in realism. This has repercussions about realism throughout Essos, of course.