It is coming up on two years since the United States finally fully exited the battlefield in Afghanistan — a decade after the war started in the  aftermath of the September 11th attacks. The war is one of the longest in American history, roughly double the time the nation spent in both of the world wars combined. But in the context of world history, there are wars that dwarf the conflict. (Also check out: The 35 billion-dollar weapons in the U.S. Military budget.)

Some wars are quick, especially for countries who spend a lot on their military. But this is not always the case. Before technology made it possible to kill many enemies from anywhere, opposing sides could retreat, take refuge in a fortified castle, and wait to go back out and fight. This allowed some wars in the past to drag out decades and even centuries.

24/7 Wall St. has compiled a list of the longest wars in history by reviewing data and articles from various sources. In order to appear on this list, a conflict had to meet the definition of war as an open and usually declared armed conflict between political entities such as sovereign states or competing factions within the same state, such as a civil war. The conflict had to be sustained over a period of time and intended to resolve political or territorial disputes.

Click here to read about the longest wars in history