WMG: Empire Earth

The first two Russian Campaign levels are historical revisionism
When Grigor mentions that he is getting old and has no heirs at the very beginning of the third level, "Changing of the Guard," the people cheer rather than grieve. There's also mention in the briefing of the second level, "Novaya Russia," that many people are fleeing Russia because of war crimes and acts of terror being perpetrated by the Black Robes. Cue the entrance of Sergei Molotov, the true protagonist of the Russian Campaign from that point on, who ultimately stops both Grigor and Grigor II at the end of the campaign (if he didn't die before then during the last mission). By this time in his life, Molotov had become very disillusioned with the goals of Novaya Russia, where before he had idolized the first Grigor as one of the greatest men in history. The first two missions are probably what Molotov thought of Russian history, probably from a Novaya Russian textbook which of course would whitewash Grigor's atrocities during his rise to power while the rest of the campaign is a first-person perspective by Molotov himself. When Molotov meets young Grigor at the end of the last campaign mission, how Grigor acts is how he was historically as well: he was always an authoritarian. It's actually not very surprising, considering he looks a lot like Stalin to begin with.
Hitler is a nobody in Empire Earth
If I recall correctly, in the first game at least, Adolf Hitler himself is never mentioned in Empire Earth's German Campaign. Herman Goering is there, Erwin Rommel is there, but not Hitler. German history appears to have taken its historical course aside from this, with Germany being a dictatorship and all, but not necessarily a Nazi dictatorship.
Empire Earth actually portrays Alternate History
Building on the above, Empire Earth as a series is alternate history as well as a straight-up divergent timeline, as Russia is in better sorts in real-life than it was at the time of the Russian Campaign's origins. If all three games (or the first two at least) are considered one unified setting, the earliest point of divergence from actual history is the survival of the Aztec Empire, followed by the death of Napoleon, then Hitler not rising to power, an alternate Cold War in which World War III nearly begins between the United States and Soviet Union, followed by straight-up fiction involving Novaya Russia, the Cyborg Insurrection in the United States, the Maasai, the United Federation of Asian Republics, and finally the colonization of Mars and subsequent rebellion (to give a very incomplete timeline of events).
Operation Sea Lion wasn't as successful as it seems
It's commonly accepted, at least in the alternate history community, that Operation Sea Lion was so implausible that it could never have succeeded, and in fact would have made Germany lose sooner rather than let them hold on for a bit longer. The final level of the German Campaign from the first Empire Earth, seems to imply that Germany eventually wins, having conquered Britain. However, they still have America and the Soviet Union to contend with, and now have an angry population of Brits to try and keep under their heel as well.

Only the Germans didn't succeed. They may have declared Britain a province of the Greater German Empire, but that doesn't mean shit if they can't hold onto it. From that point on, they are losing the war even harder than they did in actual history. Which leads us into the American Campaign in Empire Earth II, where the Germans are quickly defeated by the Allies and divided into administrative zones, as well as being the site of a secret battle between American and Soviet forces.

Theseus' ascension was caused by time-travelers
That the ascension looked exactly like a future cyber power is no coincidence: he was kidnapped by cyber-using time travelers precisely to end the age of legendary heroes, so that humanity would be forced to learn to work together instead of relying on their leaders, accelerating their development. It also explains why it's the only mission in the campaign that involves the gods acting directly instead of dreams or inspiring their followers.