A U.S. aircraft and drone attack at Raso, Somalia, last Saturday killed a claimed 150 members of the militia group al-Shabab. Administration officials said the strike was conducted in anticipation of an al-Shabab assault on U.S. interests or the African Union peacekeeping force in Somalia, which the United States finances and advises.

Americans should be troubled by the deadly attack for several reasons.

Although the Pentagon claims that all of the victims were Islamic militants, that is hard to believe. The U.S. military acknowledged that the attack on the al-Shabab training camp occurred during a graduation ceremony. Were any civilians there? Who knows?

The assault is the latest U.S. military strike in a decades-long failed effort to install a sustainable government after the collapse of authority in Somalia in 1991. The collapse triggered a humanitarian crisis that led to many deaths from hunger and disease. Somalia now has an unelected government, protected by 21,500 foreign troops including U.S. Special Operations forces, that is under constant attack by al-Shabab.

The effort to prop up Somalia has cost American taxpayers a lot of money, including the millions needed to maintain what’s become a major U.S. military base in neighboring Djibouti.

Finally, and perhaps what should be the biggest concern for Americans, is that such a major attack on al-Shabab militants risks provoking a revenge assault on the United States

If these concerns are sound, the next questions have to be: Why was last Saturday’s attack carried out, and why is the U.S. still involved in an expensive, unsuccessful effort in Somalia?