This basic strategy „get a card each turn and avoid losing armies“ gets you from beginner to intermediate. Once every player understood this it once again is a question of who controls the southern continents. The additional two or three armies each turn add up.
Some years ago I regularly played Risk with three friends. It always started with a fight about the three southern continents. Of course, only three can get one. The left over player tried this strategy to stretch across Asia, Europe, and maybe even North America. Always careful to not cover a whole continent and raise attention. South America and Africa are in constant conflict with each other so they are busy with themselves. The problem is Australia. That player also needs a card every card and will constantly tear into Asia.
At some point the balance between South America and Africa will break and the northern player needs to intervene there as well. So it is impossible to not be dragged into fights and some armies need to be spent.
With four players there is always someone who will point out to your neighbors what they are overlooking. That makes the game drag on because whenever one is about to overpower another player, two others will intervene. Apart from the cards on your hand there is no hidden information in Risk. So if you play for world domination everything is very obvious all the time.
What ends the game is that the card bonus armies become so huge that every turn there is some crusade across the whole board until some is the lucky winner.
I was thinking this as well. It assumes the other players are naiive to your strategy and will not counter it. If someone were gathering a collection of bonus cards I think this would tip off the other players and awaken the dragons.
