[soah]

Taking Australia is my preferred method. After devoting a little bit of my army to defending that border, I'll keep all the rest of my units together and repeatedly attack an undefended country on each turn to receive a card. If there are enough people playing, it's usually very difficult for anyone else to control any of the other continents for more than one turn. You can stockpile units faster than anyone else, and no one can attack you without sacrificing most of their own army. Eventually you'll get an opportunity to make some sort of a move to put yourself in control of the game.