Cinco de Mayo is not an official US holiday; the reason the Battle of Puebla has become the penultimate holiday for Americans of Mexican descent is beyond me.
We do study world history. The Armenian Genocide, the Young Turks, the Crimean War, the rise of the Zulu Kingdom, all of that showed up in college. A great deal of it showed up in high school. And in the freshman year of high school we had world geography which covered physical, cultural, and economic geography. We even learned about how the Brits in Austraila hunted the natives for entertainment, not unlike our own collection of morally bankrupt Gold Rush types who did the same thing.
Where one goes to high school makes a great difference. The high school I attended was considered one of the better schools in not only the state, but the nation at the time I attended it. Now it is very poorly rated and many of the students are the children of illiterate immigrants. In 1998 the school was still reasonably highly rated; in the years since then the town has become heavily populated by illegal immigrants with the resulting decline in school standards and the flight of those who can afford to go elsewhere. The mandatory core curriculum is now significantly less rigorous.