The reason why Great Britain and France declared war on Germany at the beginning of the second World war was because A - The invasion of Poland.
When Germany invaded Poland this was the beginning of what would later be called the second World war. A tense atmosphere was brewing up in Europe for a few years since then already because when Hitler's party took charge of Germany, it increasingly militarized the country and was preparing it for war.
-people wanted to move because they wanted better lives. they faced dangerous journeys .
-they moved west because land was cheap or free and they thought they would do better business in the west .
-people who weren't making business or wasn't making any money, found the opportunities to move west to start everything all over again
I believe it was France in the D-Day Invasions, that was a massive assault on the beaches and ended in the Allied forces pushing through the Nazi defenses.