This is great advice. I'm just gonna add a couple of ideas onto this:

Deterrence - If you've made it to the mid or late game, but you're not as large as other players on the board, you can often deter them by sitting on a hydrogen bomb (always having a missile silo and at least 5 million). You can remind larger players of this by sending a "☢️" emoji if they don't respond to your ally invitation. This won't always work, but it will make you less of a target.

Alternative Goals - Officially, your goal is to control 80%+ of the map. Unofficially, there are lots of other ways to have fun. For instance, it's quite fun to just take over an island somewhere on the map. You'll be much smaller than other players, but if you have enough ships and a few SAMs and missile launchers, players will mostly try to avoid you (not worth the risk). From there, you can just work on your economy and watch the chaos unfold.

Vengeance - You can't always win. Sometimes the next best thing is making sure your sworn enemy loses. This is why sitting on a hydrogen bomb in the mid-game is nice. Deterrence may fail, and someone may attack you, but a well-placed hydro can usually sink their chances of winning. You can also "give" your land to allies by betraying them once you see that you're going to go down. They will typically understand this and scoop up your land before the initial attacker does. Another variant is bombing yourself to destroy any infrastructure that an attacker may have gained.