I would cash in the cards. I will put 4 in Scandinavia and 6 in Ukraine (consider them as insurance!).
I will then make a nonaggression pact with Blue for Greenland, with the condition being that I will take Iceland from him. It is very unlikely that he will reject, as his position is utterly terrible. So, he will accept my offer.
Then I shall wait. I would cash my Europe bonus and slowly grow. Yellow needs continents. So he may like to go for Africa since it is small and easily reachable. A few turns later, Yellow will assault the Middle East (probably winning) and moves his troops to that conflict area. I will then slowly try to grow in Asia getting one country after the other. I will make sure that Yellow doesn't get too upset, so he can carry on his assault on Green and leave me alone. In fact I will passively encourage him to do so (I can't talk about it actively, because I have a treaty with Green and I don't want to upset him either).
Meanwhile Blue is in war with Green. Green will eventually collapse as a result. At this point the situation is as follows:
Yellow gets Africa and may go for South America as well, either for the continent, or for Green's cards.
Blue owns North America, and probably likes to get South America as the Yellow troops are probably thin there.
Green is gone.
Both Blue and Yellow are probably exhausted. This is the chance I was waiting for! I shall attack Blue from Kamchatka and Iceland and try to take Blue out in one go. I get his cards and I will end up in a much better position than Yellow.
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