Wouldn't Australia be a better place for them to build a base and have a staging ground to assault the last city, I mean yes London has a natural defense but the cabal could land multiple cruisers there ( not saying London/Britain is to small for their ships ) Australia would also provide a larger play space do to sheer land mass. ( and before you assume I'm Australian, I'm Canadian so I'm not biased eh)
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no point...you can't even get Air past their Borders