The German telegram to Mexico and the sinking of U.S. merchant ships.
German invasion of Poland
the colonists went to war with Great Britain to protect their rights as English citizens
The French and Indian War
French and Indian War
because, when Belgium was invaded, it brought Britain into the war
The fall of the Soviet Union
the battle of Britain
Napoleon's conquests in Europe brought Britain, as well as Austria, Russia and many other countries, into war with France.
Boycotts/embargos.
The German violation of Belgian neutrality (invasion of Belgium).
Germans alliance with Britain