Blue will start to grow slowly over Asia. At any rate he will not be someone to worry about until later stages of the game. Yellow has two main choices: To go for Europe, or South America. He is experienced, so would think hard before initiating an attack. Since he is a negotiator, he may listen to my offers of treaties. There is a possibility to get treaty over the Brazil border.
Green will initially be interested to conquer Europe. After that he may not have much experience to know what to do. Yellow may have to keep an eye on him as he wouldn't want a strong neighbour next door. Brown is unpredictable, there is no chance to make an agreement over Central America. Hence, there will inevitably be a war taking place between me and Brown. Controlling Brown seems to be the key to success.
Killing Brown is my main aim . Once he is gone, I can have a much more stable region. However, I don’t necessarily want to fight him myself alone. First, I need to engage in a diplomatical exchange with Yellow over Brazil border. I would make an attempt to have a treaty there. Yellow can be interested since he can simply focus on a bigger prize such as Europe.
Once my African border is secure I can concentrate my entire armies on one front. Brown will be in trouble. He doesn’t have a continent and has three borders to protect as he is yet to claim the continent. My expansion in North America can continue until I get the whole continent. I would then be in a very good position to lead the game.
There is always a risk associated with any deal. Putting some deterrent armies in Brazil can offset Yellow's temptation to break the treaty.
Once I get North America, I can become a bit weak as a result of fighting. This is a critical time. I need to offset any potential attack by propaganda, because that’s all I have. I hope that Green and Yellow will be fighting each other and they would be busy enough to ignore me. I can always advice Green on his moves, so he can become a stronger opponent to Yellow. Though, this needs to be executed in a delicate way as not to upset Yellow.
If Yellow started to become a problem, I will put my armies in Iceland instead of Greenland. This doesn’t cost me much, but I have nailed Europe. Furthermore I can always go and nail North Africa if Yellow starts a full scale war on me.
Lets not forget about Blue though. If Blue decided to attack me, I will use diplomacy to bring his evil actions to the attention of other world leaders so he can be dealt with.