A Mexican unit crossed the Rio Grande and ambushed an American patrol
one event that led up to the revolutionary war is the Boston Tea party. :)
Germany... Germany sent a letter/telegraph to Mexico , which said that if Mexico allied to Germany , Germany would've recovered the territories that Mexico lost in a war with U.S ... U.S. intercepted this message which was the last event that "forced" U.S. into war...
Texas
The assassination of Archduke Ferdinand was a major event that led to WW1
The Bolshevik Revolution was the event that led to Russia's early exit from World War 1. It was a costly war for Russia.
collapse of the Soviet Union
The civil war.
There were several of them. Two instances include:The annexation of Texas as a state in 1846 led almost immediately to border conflicts that escalated into war.The occupation of the port of Veracruz in 1914 to prevent an arms shipment to reach Mexico (it did, by the way). Mexico was in the middle of it Mexican Revolution, so it couldn't respond accordingly, but this event led both countries to the brink of war and damaged relations for decades.
Civil War
the XYZ affair
pearl harbour
James K. Polk.