Read! :D

Grab a couple of bigger picture books and get a sense of the general topics people talk about within "American intervention in communist Cuba." (I'm assuming that topic, on its face, is too broad for a seminar historiography paper). American policy decisions in Washington, agents on the ground, Cuban response, effect on local population, effect on expat communities, within the overall international diplomatic system...as you read, some theme or topic or something will jump out at you. Follow the footnotes!

For a history research paper, I personally like to bounce back and forth between secondary and primary sources as I'm narrowing in on a topic, a question, and finally a thesis. The secondary source will use a primary source/set of them, I'll read those or figure out what they say from other scholarship; then I'll be inspired to go on some tangent in secondary scholarship by whatever in the primary; then the new secondary one will help me see something else in the primary...and so forth.

For a historiography paper, it can be really helpful to look at some recent PhD theses on your broad topic. They can help you get an idea of what the biggest foundational works in the field are, and more importantly, some of the shifts in the historiography over time (like when women's history hit, the evolution from social to cultural, etc).

But basically, you gotta start with reading.