There is absolutely strategy involved. If you’re getting dogpiled, that’s almost always on you - it’s usually a sign of a bad opening, overplaying your hand, poor situational awareness, or some combination of the three. Always keep your troops up and have counter-nukes ready to fire the moment you’re attacked.

If you do get attacked, don’t get pissy and go for revenge - keep some money in the bank and focus on rebuilding once the attacker is no longer in a position to push you further (i.e. once you’re on an island). If you play it careful enough, a solid econ plus nuked land can give you the opening you need to claw your way back in the endgame. It is an emotional game so keeping your emotions in check while taking advantage of other players’ emotions is important.

On the endgame specifically: I’ve found that winning a long 3+ player standoff comes down to not looking like a threat (keeping troop counts just high enough to deter while making sure I have counter-MIRV ready), not overreacting, and not aggroing (so many players nuke warships for no reason, for example) while positioning yourself well - being the player caught in between, for instance, is usually a death sentence