What action by hitler prompted great britain and france to declare war on germany?

The joint invasion of Poland by Germany and the USSR,

despite what people may think Germany invaded multiple smaller countries before invading Poland, it was a slow buildup but Poland was the last straw.

Explanation:

whose power in the senate is equal to the power of the speaker of the house?

new evidence is discovered.

oversights and errors are corrected,

new technology is applied to evidence.