"The idea of a European military didn't work out too well in WW I or 2. But the US was there for you, and always will be," Trump said in a tweet.
His comments came amid moves by certain European countries to have a combined European military so as to reduce their dependence on US forces in the region.
Ever since coming to power, Trump has been demanding that European NATO allies increase their contribution to NATO to two per cent of their GDP.
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