How true is the adage that there are none so blind as those who will not see. Jackson Diehl, in his Dec. 8 op-ed column, “The sloppy thinking of ‘no military solution,’ ” brought to light again President Obama’s lack of leadership and his acceptance of advice from those who lack international expertise. Imagine if Mr. Obama had been president in 1941 and, following the attack on Pearl Harbor or the declaration of war on the United States by Hitler a few days later, he addressed the American people and told them that there was “no military solution” to the events in Europe and Asia. Where would the United States be today? Where would Europe and Asia be today?

The problem of Nazi Germany and imperial Japan was solved by military, not diplomatic, means. As long as one is confronted with an ideological threat, such as that posed by Nazism 70-plus years ago, and radical, fundamentalist Islam, such as that posed by the Islamic State, Jabhat al-Nusra, Hezbollah and Hamas today, the only solution is the destruction of those entities by military means. Only then can diplomacy take over to combat the ideology.

Sheldon Goldberg, Silver Spring

Jackson Diehl’s endorsement of the use of force as a central tool of U.S. foreign policy and his claim that “political solutions are often dictated by military conditions” are backward. More often than not, military action creates new problems and prolongs existing conflicts. One egregious example of this phenomenon is the George W. Bush administration’s disastrous decision to invade Iraq. But lesser interventions in Yemen, Pakistan and Somalia have likewise done more to sow chaos and foster anti-U.S. sentiment than they have to resolve the conflicts there. Even allegedly positive examples, such as the arming of the mujahideen in Afghanistan to fight Soviet occupation, have had severe unintended consequences, such as the strengthening of individuals and groups that went on to form al-Qaeda.

Mr. Diehl made another error in assuming that major conflicts in one area hinge on whether the United States has shown its resolve by sending troops, bombs or weapons into a conflict in another region. Russia would have acted no differently in Ukraine if the United States had bombed Syria. And China’s assertiveness in the South China Sea is tied to interests that long predate the Obama administration.

William D. Hartung, New York

The writer is director of the Arms and Security Project at the Center for International Policy.