This blog post was coauthored with my research associate, Jennifer Wilson.

[Note: This post was updated to reflect an additional strike in Yemen in 2016, announced by U.S. Central Command on January 12, 2017.]

As President Obama enters the final weeks of his presidency, there will be ample assessments of his foreign military approach, which has focused on reducing U.S. ground combat troops (with the notable exception of the Afghanistan surge), supporting local security partners, and authorizing the expansive use of air power. Whether this strategy “works”—i.e. reduces the threat posed by extremists operating from those countries and improves overall security and governance on the ground—is highly contested. Yet, for better or worse, these are the central tenets of the Obama doctrine.

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In President Obama’s last year in office, the United States dropped 26,172 bombs in seven countries. This estimate is undoubtedly low, considering reliable data is only available for airstrikes in Pakistan, Yemen, Somalia, and Libya, and a single "strike," according to the Pentagon’s definition, can involve multiple bombs or munitions. In 2016, the United States dropped 3,028 more bombs—and in one more country, Libya—than in 2015.

Most (24,287) were dropped in Iraq and Syria. This number is based on the percentage of total coalition airstrikes carried out in 2016 by the United States in Operation Inherent Resolve (OIR), the counter-Islamic State campaign. The Pentagon publishes a running count of bombs dropped by the United States and its partners, and we found data for 2016 using OIR public strike releases and this handy tool.* Using this data, we found that in 2016, the United States conducted about 79 percent (5,904) of the coalition airstrikes in Iraq and Syria, which together total 7,473. Of the total 30,743 bombs that the coalition dropped, then, the United States dropped 24,287 (79 percent of 30,743).

To determine how many U.S. bombs were dropped on each Iraq and Syria, we looked at the percentage of total U.S. OIR airstrikes conducted in each country. They were nearly evenly split, with 49.8 percent (or 2,941 airstrikes) carried out in Iraq, and 50.2 percent (or 2,963 airstrikes) in Syria. Therefore, the number of bombs dropped were also nearly the same in the two countries (12,095 in Iraq; 12,192 in Syria). Last year, the United States conducted approximately 67 percent of airstrikes in Iraq in 2016, and 96 percent of those in Syria.

*Our data is based on OIR totals between January 10, 2016 and December 31, 2016