Academically: whatever your university's history degree program mandates. Without knowing which university you plan to attend/are attending, anything more specific is impossible. However I will try to give a very general overview, under the assumptions that you are 1) seeking a Bachelor's degree and 2) the university is located in the US.

Undergraduate history degrees are typically fairly open ended, requiring some total of history credits/hours to receive the degree. Some universities require a senior thesis, while at others it is only necessary for graduating with honors.

The history program is likely to mandate that you take some blend of European history and non European history. Some universities hold US history as separate category and mandate a minimum amount of US history hours as well. Others further require that students take at least one modern history course and one pre-modern history course.

Personally: your own interests.

I’m interested in war/conflict history, but should I be learning about.. say marketing history

That depends on what you intend to do after graduation. Grad school? Diplomatic work? Private sector? Think tank?