What is the three key events for america moves west

Land. Lots of land.

The Louisiana Purchase of 1803 intensified American migration to the west that was already well underway. Anglo-American settlement in the 18th century had largely been confined to the eastern seaboard. It made its boldest inroads where rivers allowed easy internal transportation. As a result the chief population centers of early North America were clustered on the coast or along its major inland waterways.

i see, would you mind putting it as one?

a king decides to declare war on a neighboring country without the input of any advisers