U.S. missile defense in the twenty-first century is focused on emerging threats from North Korea and Iran, but critics say these systems are too costly and largely unproven, explains this Backgrounder.

The Boston Marathon bombings illustrate the stresses on domestic intelligence gathering and counterterrorism in a democratic system, says CFR's Richard Falkenrath.

The deadly bombings at the Boston Marathon raise anew the vulnerability of U.S. civilian targets and homeland security policy dilemmas, as examined in this CFR Issue Guide.

What is the Obama administration's legal justification for targeted killings? CFR national security expert John Bellinger explores this question as well as others with significant implications for U.S. counterterrorism.

In the wake of the U.S. withdrawal, a resurgent al-Qaeda in Iraq, allied with jihadist fighters in neighboring Syria, constitutes a considerable threat to regional security, explains this Backgrounder.

As the Pentagon attempts to refocus the U.S. military strategy toward Asia, the department is facing major budget constraints. Experts disagree on how to balance the fiscal challenge with the country's national security priorities.

Some experts believe al-Shabaab is at its weakest point in years following an African-led counterinsurgency campaign, but others warn of the group's resiliency in an unstable Somalia.

Admiral Dennis Blair and CFR's Micah Zenko discuss U.S. drone strike policies.

Why do mass shootings, such as the December 2012 incident at a Connecticut elementary school, occur more frequently in the United States than other major democracies? This Backgrounder examines select countries.

As the U.S. approaches the deadline to raise its debt limit, economists warn of a fiscal crisis and steeply higher borrowing costs for U.S. businesses and homeowners.

The quest by Palestinian officials for statehood recognition could have major repercussions for the Mideast peace process. This Backgrounder outlines the potential impact of the UN vote.

While congressional action lags, a series of year-end fiscal measures could derail the U.S. recovery. This Backgrounder examines the potential global impact.

International efforts to ease Syria's crisis have been limited by divisions in the UN Security Council and wariness about a military response, explains this Backgrounder.

The expansion of North Africa's AQIM into Mali and links to attacks against the U.S. consulate in Libya have spurred fears about the group's threat to the region, explains this CFR backgrounder.

Many states and cities face significant fiscal stress that could impede the U.S. economic recovery and undermine long-term growth, including cuts to education and infrastructure, explains this CFR Backgrounder.

The Arab Spring severely weakened the narrative of Islamist extremists but they are now stirring anti-U.S. sentiments in fragile new democracies, says Mideast expert Ali Soufan.

Post-9/11 U.S. counterterrorism and surrounding civil liberties issues are unlikely to stray far from currently policy no matter who is in the White House in 2013, says CFR's Matthew Waxman.

A post-Assad Syria will likely create distinct challenges for each of its neighbors, including creating a major loss for Iran, says Michael Young of Lebanon's Daily Star.

The People's Mujahedin of Iran, or MEK, is a militant Iranian opposition group and a recognized terrorist organization, according to the U.S. State Department. This Backgrounder examines the group's history and the politics surrounding its relocation from Iraq.