The United States has long urged its allies -- particularly European governments -- to spend a greater share of their budgets on defense. American officials have warned that defense cuts in recent years by many members of the North Atlantic Treaty Organization have created a two-tiered system in which some nations are freeloading off of those that continue to invest heavily in defense.

Several capitals have done little more than pay lip service to warnings from Washington, which continues to spend approximately 4 percent of its gross domestic product on defense. The United States has shouldered a higher share of NATO’s defense expenditures in recent years. According to NATO’s 2013 annual report, Washington was paying 73 percent of the alliance’s defense expenditures, up from 68 percent in 2007.

NATO leaders have demanded that members spend at least 2 percent of their GDP on defense, but several have struggled to meet that threshold. Currently, few European countries are meeting that benchmark. By way of comparison, Russia spends 4.5 of its GDP on defense.

Here’s a look at how European countries -- both in and out of NATO -- and how much of their GDP they spent on defense in 2012 and 2013, based on World Bank statistics. (NATO countries are marked with an asterisk.)

Georgia: 2.9 percent

Britain*: 2.3 percent

Greece*: 2.6 percent

France*: 2.3 percent

Poland*: 1.9 percent

Portugal*: 1.8 percent

Italy*: 1.7 percent

Bulgaria*: 1.5 percent

Finland: 1.5 percent

Denmark*: 1.4 percent

Norway*: 1.4 percent

Germany*: 1.3 percent

Sweden: 1.2 percent

Belgium*: 1.1 percent

Lithuania*: 1 percent

Spain*: 0.9 percent

Switzerland: 0.8 percent

Austria: 0.8 percent

Hungary*: 0.8 percent

Luxembourg*: 0.6 percent

The disparity in defense spending became clear when the U.S. and some allies took the lead in backing rebels seeking to oust Libyan leader Moammar Gaddafi in 2011. Then-U.S. Secretary of Defense Leon Panetta said the operation had revealed just how reliant the alliance remains on the hardware and coffers of just a few members.

“We need to use this moment to make the case for the need to invest in this alliance, to ensure it remains relevant to the security challenges of the future,” he said in a speech in Brussels in October 2011.

The issue has received renewed attention in the wake of Russia’s annexation of Crimea.

The World Bank also has a helpful map and table with spending data: