Fallacy

a relatively insignificant first event is to lead to a bigger event, which then becames a bigger event, and so on, until some ultimate, significant event is reached, but with each step it becomes more and more improbable.
Ex: 

1. "The US shouldn't get involved militarily in other countries. Once the government sends in a few troops, it will then send in thousands to die.

This sort of "reasoning" is fallacious because there is no reason to believe that one event must inevitably follow from another without an argument for such a claim

https://youtu.be/BtckZ7CLBFI