Why were there no invasions of Macedonia or Greece while Alexander was in Asia?

Thanks to Valentine for sending this in. 'I have finished rereading your excellent article, “Men you can Trust,” in Volume 16, Issue 6 of Ancient Warfare. A question arose in my mind that you may be able to answer. With the bulk of Alexander’s army in Asia, and especially India, why did no foreign invader seek to take advantage of the situation by invading parts of Macedonia?'

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