World War I was a truly global conflict. Networks of alliances forced countries to become involved in the fighting, even if they did not directly have a stake in the conflict.
Pearl harbor
Pearly Harbor
there is no clear event because Germany still kept on fighting in various areas
World War II.
Germany in WW2 had many fronts but i think what you are asking that in Europe since 1941 was fighting the Soviet Union, in 1944 the allied forces landed in Normandy, France which forced Nazi Germany to fight on both fronts but Germany was also fighting in North Africa and Italy until the Normandy landings.
Quebec's armies joined in on fighting overseas in WWII. However, it was strictly on a volunteer basis. Quebec's people were against Conscription [being forced into fighting].
The Japanes attack on Pearl HarborThe German declaration of war on the US
Germany was TOO imperialistic, and they forced Britain into the war.
the assassination of Archduke Franz Ferdinand in Sarajevo, Bosnia on June 28, 1914.
The arrival of Commodore Perry in 1853, followed by the Harris Treaty in 1858.
The Axis was the event that formed the alliance between Italy and Germany in World War II. Italy was forced to sign under the threat of an invasion.