The United States currently pays for 75% of NATO expenses (hardware, logistics, trans., manpower, etc).
70 years after WWII, the largest European nations - individually and as NATO members - have consistently refused to increase their defense budgets, content to let the U.S. provide the bulk of what is necessary for their defense.
The EU is a fragile construction at best with continued wrangling over cooperation between member nations and how much power the EU parliament in Brussels should wield.
Whether EU nations individually begin to take more responsibility for their own defense or in concert with other member nations, the U.S. can not afford to continue our subsidies at the current levels.
http://www.bbc.com/news/world-31619553