Under what circumstances might conscription be necessary?

I assume your question refers to The United States in our current circumstances, i.e. the War on Terror. I come from the Cold War generation that faced a universal draft. In fact, I volunteered for the army because I knew if I didn't I'd be drafted. I served through the Cuban Missile Crisis and the Berlin Wall. I was serving when President Kennedy was shot and we weren't sure whether there was a conspiracy or if the Soviets were involved. We didn't stop the draft until 1973, just two years before we finally gave up and got out of Vietnam.

Under what circumstances might conscription be necessary? Whether you agree with the war in Iraq or not, the bottom line is that our all-volunteer military is stretched perilously thin in Iraq and Afghanistan. We have not been able to capture Osama bin Laden or any of his higher ups. The War in Iraq has nearly sucked dry the energy of all the Armed Forces. We are extending tours for our soldiers, and some of our troops have done three tours so far in either Iraq or Afghanistan, with no end in sight. The troops we have are becoming exhausted, and enlistment rates are down, especially for the army.

Despite the Pentagon's own admission that our self sacrificing volunteer troops are nearing the breaking point, the present administration is rattling the saber at both Iran and North Korea over nuclear weapons and other issues, especially the mounting evidence that Iran is providing deadly weapons and training to terrorists in Iraq. Should we somehow end up in a war with either or both, where would the soldiers come from? It's at that point that I think conscription might be necessary. It could even become necessary should enlistment rates fall to the point that we can no longer supply the troops to keep up the "surge" in Iraq, if the next administration chooses to continue the fight. If the all volunteer force is too small and depleted to do the job, history shows that the government is likely to turn to conscription. It did in the Civil War and both World Wars, not to mention The Cold War and Vietnam.

The really big question is, what happens if the government tries to reinstate the draft? How many young people would obey the law? How many would burn their draft cards or flee? Do we conscript women? Should women fight? (They do now.) Do we have to agree with a war in order to fight it? Can those who don't agree say No? These are all questions I personally hope we never have to answer.