The US spending so much on European security allows Europe to have stronger social safety nets and many European style programs without significantly stressing

The US spending so much on European security allows Europe to have stronger social safety nets and many European style programs without significantly stressing their budgets. As you noted, spending is not in line with other nations on a per GDP basis. The trade is the US foots the bill but gets bases (geopolitical control) out of it. Europe gets protection which they would normally have to pay for. While currently things are strained, historically this has been an amicable relationship where both sides got what they wanted. Perhaps this will change in the future, but that is the context.