WASHINGTON: President Barack Obama unveiled a defence strategy on Thursday that calls for greater US military presence in Asia and envisions cutting troops in Europe as the Pentagon seeks to reduce spending by nearly half a trillion dollars after a decade of war. Obama, in a Pentagon news conference alongside defence secretary Leon Panetta, released a strategy document that calls for the US to maintain a force that can win one war while still having the capability to deter the objectives of an adversary in a second conflict. That is a shift away from the military's goal of being able to fight and prevail in two wars in different theaters simultaneously. The strategy also calls for the US military to "rebalance toward the Asia-Pacific region" even as it continues to actively counter the threat of violent extremism. "Even as our troops continue to fight in Afghanistan, the tide of war is receding," Obama said. "Even as our forces prevail in today's missions, we have the opportunity - and the responsibility - to look ahead to the force we need for the future". The strategy also calls for increased investment in cyber capabilities and suggests US may be able to shrink its nuclear arsenal further without jeopardizing security. The shift in focus to Asia comes amid concern over China's strategic goals as it begins to field a new generation of weapons that could prevent US naval and air forces from projecting power into the Far East. But administration officials said army and marine corps personnel numbers would be cut by 10 to 15% in the next decade. The strategy document underscores a US interest in maintaining stability in the Middle East while responding to the aspirations of the people as expressed in the Arab Awakening last year. It says US will continue to halt nuclear programs in Iran and North Korea.