AskHistorians

Mostly the first one (different war), but the lines are not always clear.

Many people cite the 1939 invasion of Poland as an event which kicked off WWII. But far fewer consider the 1931 Japanese invasion of Manchuria to be a WWII event. This is usually labeled as an event of the first Sino-Japanese war.

The confusing part is that the Japanese were basically in a war of some kind from at least 1931 until 1945. The European and American powers were basically uninvolved in any of it, until the attack on Pearl Harbor brought them in.

But the question really is: did Pearl Harbor bring the American and European powers into Japan's existing war, or did Japan join the war started by the invasion of Poland?

As other commenters have said, largely because of Eurocentrism the earlier wars are just ignored for labelling purposes, and Japan is considered to have joined WWII when they attacked Pearl Harbor.

And, in terms of interactions between Imperial Japan and Nazi Germany, they were mostly superficial. If you've thought it never made sense how two countries operating largely on racism could get together and form the "Axis Powers", you're right: that was just another label to unite the Allies against what they saw to be common enemies.

Tldr: Japan was ultimately in their own war which continued into the WWII dates; European/American bias suggests they joined WWII when attacking Pearl Harbor.