to withdraw troops

I don't think anybody really understands. It's a very complex issue. If you keep them there or pull them out it is still bad.

I heard it in VOA,maybe special English...
Thank you all the same !

Certainly, a nation can decide to withdraw its troops from combat or postings at any time. As with all decisions, there are consequences whenever troops are withdrawn from an assignment/mission. It also makes a big difference whether the withdrawl is tactical or strategic. Tactical withdrawl may have little consequence to the overall mission, but strategic withdrawl almost always has serious consequences. To abandon the battlefield to an enemy is one standard definition of defeat, and defeat is rarely a good thing in war. The overall goal is to force the enemy to withdraw, and in defeat to surrender. Withdrawl before all of a mission's objectives have been achieved is generally not advisable, since that will usually make post-conflict more difficult.

Withdrawl of troops may cause a crisis of confidence among one's clients and allies. Japan and ROK, for instance rely upon U.S. commitments to provide a defensive shield against aggression from the DPRK, China, and Russia. To remove our 35,000 troop garrison from the Peninsula would send a message to the DPRK that the U.S. was withdrawing its protection from the ROK, and invasion of the South would almost certainly follow. At the same time, Japan would have to reconsider its security and might decide to revise its Constitution to provide for a more active military and acquisition of nuclear warheads. In both these examples, the outcome of withdrawing troops would be extremely risky and might well lead to a regional nuclear exchange a few years down stream.

I've responded here to your question as written, though perhaps you had something more specific in mind. If so, tighten the focus of your query and we'll make another run at it.

Certainly, a nation can decide to withdraw its troops from combat or postings at any time. As with all decisions, there are consequences whenever troops are withdrawn from an assignment/mission.

It also makes a big difference whether the withdrawl is tactical or strategic. Tactical withdrawl may have little consequence to the overall mission, but strategic withdrawl almost always has serious consequences. To abandon the battlefield to an enemy is one standard definition of defeat, and defeat is rarely a good thing in war. The overall goal is to force the enemy to withdraw, and in defeat to surrender. Withdrawl before all of a mission's objectives have been achieved is generally not advisable, since that will usually make post-conflict more difficult. An example was the Cease Fire and withdrawl of Coalition Forces before Saddam and his forces were completely defeated. Saddam then jerked the world around for over a decade while flouting Cease Fire conditions and supporting terrorist activities. Withdrawing troops in that case was premature, and in the end led to more difficulties than it solved.

The U.S. will withdraw from Iraq, the question is when and under what conditions. Some want to remove our troops instantly, and leave the Iraqi's to sort themselves out. That would give the "edge" in the conflict to those forces (largely supported by Iran and Syria, with financial support from Arabia) that are determined that Iraq shall only be governed by their own brand of Islamic philosophy. Until the Iraqi government is strong enough, and has its own military force to combat these international outlaws and murderers, would be like turning a prison over to the sociopathic killers on Deaths Row. Not a good idea for Iraq, the U.S., or World peace in general. We could certainly withdraw, and rather quickly, but the risks and consequences would be very great.

Withdrawl of troops may cause a crisis of confidence among one's clients and allies. Japan and ROK, for instance rely upon U.S. commitments to provide a defensive shield against aggression from the DPRK, China, and Russia. To remove our 35,000 troop garrison from the Peninsula would send a message to the DPRK that the U.S. was withdrawing its protection from the ROK, and invasion of the South would almost certainly follow. At the same time, Japan would have to reconsider its security and might decide to revise its Constitution to provide for a more active military and acquisition of nuclear warheads. In both these examples, the outcome of withdrawing troops would be extremely risky and might well lead to a regional nuclear exchange a few years down stream.

I've responded here to your question as written, though perhaps you had something more specific in mind. If so, tighten the focus of your query and we'll make another run at it.