Basically, between 11 and 13 we learn about everything major up to World War I. At 16 we learn some about the stuff between WWI and WWII, but mostly everything from WWII to the 1970s. Even cultural things about those eras.
It goes (and I'm leaving out some details):
Native Peoples in each region of the US and how they lived (there are a freaking lot of them, but there's a focus on the major ones such as the Iroquois).
The colonial era from Columbus on to the American Revolution in the late 18th century. Of particular note was the colonial sides of the Seven Year War in the 1750s and 1760s and the events that led to the American revolution.
The American Revolution.
The formation of the nation and its early governing documents.
A bit about Europe such as the French Revolution.
Napoleon selling us a huge chunk of New France.
The War of 1812 against Britain.
The Mexican-American War.
The climate leading up to the American Civil War.
The Confederate States of America.
The American Civil War.
President Lincoln's Assassination.
The "golden age" of American expansion and immigration, where the "Wild West" was settled and hundreds of millions of immigrants really started coming in droves because rumors spread that our streets were paved with gold because there was so much opportunity and wealth.
The Titanic.
World War I and the influenza epidemic.
The Roarin' 1920s.
The Great Depression/Dust Bowl years.
World War II on the British/American fronts.
The 1950s and the Red Scare.
The 1960s and the Civil Rights Movement.
The 1950s/1960s and counterculture.
The Vietnam War.
The Watergate scandal.