In the aftermath of the failed revolutions of 1848-49 a number of liberals fled to the U.S., especially from Central Europe. However, at that time migration was already in full swing anyway. So, there is room for debate as to how many 'extra' migrants went to America for political reasons at the time. (Large scale migration from the German-speaking lands grew sharply from about 1830 onwards, and is often cited as one of the reasons for the establishment of the Hamburg-America Line (HAPAG) in 1847. This predates the failed revolutions).
political conflicts
the assassination of the Archduke Franz Ferdinand
The defeat of the Spanish Armada caused England to win the war against Spain.
the cold war
Columbus discovered America.
nothing
your mon
The mysterious sinking of the USS Maine.
The attack on Pearl Harbor caused America to join World War II which is when they began to research and develop the bomb.
The election of Barack Obama
The election of Barack Obama
One big event that happened in America during World War 1 was that the economy started to improve. Industry also picked up during this time.
holocaust
Financial crisis
The election of Barack Obama
The launch of Sputnik.
If you are asking this question you probably have herpes.
Every event that ever happened caused another event to happen. Be specific.