How do you write a geopolitical plot if your novel is short? Geopolitical plots tend to be complex, so I am wondering if there are ways to fit the plot into a short novel or make change the formatting or how a novel is told so that it fits a complex geopolitical plot to insure that the geopolitical plot fits a short novel or novella.
Geopolitical plots are often heavy on the word count, partly because the situations tend to be quite complex and partly because the machinerey of geopolitics doesn't often move very fast - but they don't have to be that way.
You could write a novella or even a short story that focuses on one particular event or period of time that has wider reaching impact, for example you could cover day or two's worth of intense 11th hour treaty negotiatons aimed at averting or ending a war that sort of thing. It really wouldn't need to be particularly long to cover it well, think a geopolitical version of 12 Angry Men.
Since you would want to avoid a need for extensive exposition to get the reader to understand the wider picture you can use either a well known existing situation (contemperary or historical) that the reader is likely to have some pre-existing knowledge of or you can use a thinly veiled expy of one and use that as the backdrop to the pivotal events you're actually having take place in the story. Taking a real-life example, consider the Cuban Missle Crisis of 1962, sure there's a decade or more of slow-moving political tensions leading up to it but the events of the crisis itself happened over thirteen days, a fictional tale of a similar situation could take the same well-known "big picture" of the cold war (which would require essentially no explanation to the reader) and throw a fictionalised version of US and Soviet leaders of the era together in a secret two-day conference. All the heavy lifting of setting the scene, establishing the stakes and so on will have already been done for you by history and as a result you can focus your story very tightly.
From there you just follow the typical playbook for writing shorter novellas, avoid subplots etc and you're right on track for something that fits in 35-45,000 words easily.