At the moment, Poland is the NATO member state spending the most per GDP on defense investments, according to the latest data from the alliance, at 4.12 percent. Estonia follows with 3.43 percent and the U.S. places third with 3.38 percent. Conversely, Belgium, Canada, Italy and Spain each spend less than 1.5 percent.

President Donald Trump Wednesday reversed course on his longstanding skepticism of NATO, hailing the trans-Atlantic military alliance as "not a rip-off" at a summit in the Netherlands. Member nations pledged to increase their military budgets to 5% of GDP in the coming decade,