At present, the United States military maintains bases in many countries around the world. An exact count is not possible due to the covert nature of some of these bases, but the United States does maintain bases in most friendly countries. How many of these bases are actually needed and how many can be closed down? First, let's look at how some of these bases both within and outside the US came to be.
Most US Army, Navy, and Marine Corps bases within the United States either date to the 1800s or the Second World War buildup. Some, like the West Point Army Academy and the Norfolk shipyard date to around the Revolutionary war. These bases have been consolidated over the years to a small number of large bases.
All these bases are not needed, but I believe that most are needed. Certainly we need at least one major base in as many climate zones as we can find in the United States to better prepare soldiers for the conditions they will experience overseas. In addition, closing a base within the United States has an enormous effect on the surrounding area and often keeping the base running generates more money than would be saved by closing it.
Air Force bases are a different story as all were built before WWII or during the early cold war. Bomber bases were built deep within the United States to better protect the bombers from Soviet aircraft. Their placement was made obsolete by developing missile technology, but due to the enormous infrastructure currently in place, many of these bases should also be maintained. It is only overseas that large cuts can be made.
Overseas bases are a source of controversy, both at home and abroad. While they do provide a boost to local economies, just like at home, they can cause resentment and outright hatred of the United States whenever incidents occur. Some are needed to maintain the US network that allows us to reach troubled regions quickly, but many are not. Europe is the home of a great many US bases and where many are not needed.
The United States has bases in Europe dating back to WWII and the immediate aftermath. The US Army personnel in Europe are largely not needed, and virtually all of those bases can be closed. Instead, a few select super-bases like Ramstein Air Base should be kept running. These few large bases serve as hubs for an air network that allows US forces to move around the world. If possible, US bases in Europe can be merged with NATO and local bases to better strengthen connections with allies. Each base should be examined to see how it fits into the network. If it is not needed, it should be sold off and the personnel either sent to a more important base or returned to the United States.
Asia is the region where nearly every possible challenge to the United States is located and where the US is involved in active combat operations. In addition, the oil supplies of the Middle East requires protection from Air Force and Navy units. However, this is also the region with the greatest hatred of the United States and where bases increase that anger dramatically. Turkey is a friend of the United States and we possess several bases there. At least one should be maintained to keep the air network running, but the rest are not needed. Similarly, bases in Saudi Arabia and the other Gulf states are not needed. This entire area can be supported by the US Navy, Diego Garcia in the Indian Ocean, and bases in Europe.
On the other side of Asia lies Japan, China, and South Korea. Because of the current state of affairs with North Korea, bases in South Korea must be maintained at present. However, bases in Japan are not needed as Guam is US territory and there are several bases in the Philippines, as well as Australia. The only other purpose of US bases in the western Pacific is to watch China, which is rapidly becoming a regional power. In fact, many of China's neighbors which were hostile to the United States have now asked us for assistance against China including Vietnam. Only a few large bases in the Pacific and the US Navy are needed in the Pacific and Indian oceans.
Africa has always been the forgotten continent by the United States but we do currently possess a number of bases there. Resources from Africa are considered important to the United States and military forces are assisting African militaries in training and modernization efforts. Finally, South America is also home to a small number of US bases. Many of these bases are the result of training missions to these countries, especially in Columbia. Because of the close distance between the United States and South America, few bases are needed there. The only conceivable threat to the United States there in Venezuela and they really are not a threat.
The United States is currently overstretched in terms of funds and military resources. Every base within and outside the United States must be examined to see if it is needed. First, the Pentagon needs to define a network of airbases around the world. Then, look at the large remainder and see how many are still needed. I imagine the number that are still needed will be small. The US Navy can support the US mission around the world much more effectively and will cause significantly less hatred against the US. Funding freed up by this effect can both be used to reduce the deficit but also to provide additional funding to the two most needed branches, the Navy and the Air Force.