Near the end of Strat 3 I proudly supported my slavic brothers on their invasion of NA, as DRZ wiped out every fief of my former allies and Union stayed to occupy the ruins in the heartland of TKoV's claims, defending on NA ping until the end of Strat.
It was actually really fun, but I was just about the only person mercing on UIF side from NA for most battles, shit talking fat stupid Americans the entire time. Seemed like just about no one in any of the UIF clans enjoyed the battles though, since everyone had horrible latency (despite the fantastic gear.)
Also if I recall one of the main reasons they invaded NA was because they had no one left to fight in EU, since the western European clans are almost all pussy quitters who bail out of wars and destroy their own tickets and gold instead of showing up to their own battles once they start losing.
Main thing to remember is that Strat 2 was by far the best. I doubt anyone who was active at the time would disagree. It had simple map mechanics that remained balanced, so clans could easily develop themed armies with appropriate gear levels, and not get burnt out sperging over dots on their Internet Explorer 8's. NA and EU clans had fluid alliances, finding cross time-zone merc support, bailouts of gold and tickets, and hilarious scheming sessions in TS.
I was an LLJK officer at the time and worked with UIF at its multinational criminal conspiracy prime to absolutely crush at least a dozen clans, including the complete destruction of the Shogunate as an entity (I personally led the invasion of their EU heartland, crushed their armies, mocked their gimmick, and posted youtubes of their shame until their seppuku). This UIF alliance didn't even have Grey Order or DRZ contributing anything except sharing a friendly border, those clans (Bashibazouk, Risen, Legio, Union, maybe some others) were just cool people with good organization who enjoyed shitting on their enemies on the forums and in game.
I think bringing back the shared map, and simplifying Strategus mechanics to make battles more frequent, less demanding of behind the scenes sperging, and generally a more "casual" feel would be the only thing to keep the game alive. Then people could send armies into the Slavic hivemind to take out their fiefs and not quit the game for 12 months when they lose a few times.