@Tookey76 - Won 424587 on Hard with Green first attempt. First move go west to start claiming those cities and the port there. Second turn send one guy north of your city, but then retreat, don't try to take/hold that port. Just build a stack close to home to ward off Blue. Once you get a couple of the cities to the west, Purple will ally with you. Run an army to take the cities and ports in the North/central part of the map. With me, Purple took out Red and shortly betrayed me, but by that point I had enough cities, ports, and armies to defeat him. Blue kept sending troops, but the capital and nearest city usually produced enough troops to easily hold him off (occasionally getting support from a city to the west).
I think it took me about 38 turns, but I'm vindictive and make sure to kill an ally who betrays me before anyone else.
@ChangW3 - On hard. I just did it again to make sure. Green and Blue got close to killing me this time, but I managed to kill red and bring down some reinforcements. If blue is near your capital, he probably won't bother you if you run a small army to capture the ports up top. That will help morale and troop generation.
For red, moves 1-4 were: straight up, then grab city, and move toward port. Red will take the city, but you'll be able to take it right back. There will be some give-and-go around those cities between you and red, but if you can build up an army of 30-40, try to sneak along the coast, maybe grab one of the ports, then a city by red. If possible, sneak another army of 20 or so up so that you have two options to kill red. Meanwhile, build up as big of an army up-right from your capital.
@Generalfletch - I did map 730912 with Violet in 60 turns (though it could be done in much fewer, I wasn't going for speed). I started by going straight up to the closest city, and with the second move, I went to the right. I lost the city, but it weakened Red's army. I grabbed the port with the second guy. Then it was a grind north to take out red. I forget the moved, but I managed to build up a decent army (50-odd troops), and move SW of Red's capital, then went in for the kill. Meanwhile, build up an army of 99 NE of your capital, two if you can, to block oncoming from Green, and then Blue. Then, when Red was taken out, Blue was right there to sweep up some cities/ports, but you should be able to generate enough troops to take them back without too much difficulty. Once you have the West edge secure (send troops down toward your capital to reinforce), it's just a matter of time. Sweep through all those ports on the North middle, and the game will be over before you know it.