How can i expand and defend?

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Not sure why the image isn't uploading ...

Anyways im playing in the FFA version of the world at war map ( a big mistake because who knows when this game will finish ) I've expanded across africa and made a good ally, but how can i defend my territory? Big navy? Planes? Both? I'm thinking both. And then a few stacks in the non cores (around 40 in each sub division of africa (around 5)) and then focus on expansion.