Thought I would give a little background on US involvment in the Middle East to explain why the US acts the way it does.
Believing that US got a raw deal in its share of the spoils after World War One, the government set up a post-war planning committee out the outbreak of WWII 1939, with its essential function being to find ways to advance US interests in the aftermath of the war. The Policy Planning Staff of the State Department worked in conjucture with the Council on Foreign Relations (intellectuals and business elites) on what was called The War and Peace Studies Project.
The final report took shape when planners realized that the US would come out of the war as the most dominant country, with the rest of the industrialized world pretty much laid to waste. Being the only country with the ability to rebuild the international order, the US naturally sought to do so in a way that would preserve US economic and military dominance for as long as possible. The entire world was divided up, each region filling some specific purpose, and always under a framework where US interests would prevail. One of the most important factors in keeping the industrial world (Western Europe and Japan) in the US orbit was that they had to import all the oil that was used to run their economies/militaries; putting the US at a great advantage as it was the world's leader oil producer at the time. However the post-war planners knew US oil production would peak in about 25 years and thus did a survery around the world for alternate oil supplies. The final report stated "In all surveys of the situation the pencil came to an awed pause at one point and place--The Middle East."
Discovering the enormity of the oil in the Middle East, the State Department immediately declared it the single "greatest material prize in all of history," and if it could be controlled by the United States it could be used as a "veto power" on the rest of the industrial world, which was completely reliant that oil for its survival.
But as the 1940's became the 1950's, two big problems arose that challenged US control of the region. Soviet influence and anti-colonial Arab nationalism. The problem of Arab nationalism meant some of the Arab states (as well as Iran) had been overthrowing dictatorships installed by France and Britain and the new governments were seeking to completely expel the Western powers and regain control of their oil supplies. President Eisenhower declared that the Middle East was "strategically the most important area of the world" and therefore should be under US control, not the native population. It was hoped this could be done by propping up friendly dictatorships like Saudi Arabia and Iran. Thus when the Iranian people overthrew the US supported dicator (the Shah) the CIA quickly moved to put him back in power; although in their after report the CIA noted that unpopular US policies in the Middle East could eventually cause "blowback."
However having a few friendly regimes in the area did completely solve the problem of US control. By the middle of the 1960's the US was overwhelmed with Cold War priorities, massive civil unrest at home and particular distracted by the disaterous/unending war in Vietnam which had by then become the dominant priority. Meanwhile across the Middle East, regimes not allied to the US, led by Gamal Abdu Nasser of Egypt, were rapidly building up their military capacities (aided by the Soviet Union) under the rallying cry of a Pan-Arab nationalism, free from Western dominanation.
And then suddenly, they were all gone. In less then six days, the Israeli military virtually destroyed the entire military capacity of Egypt, Jordan and Syria. The entire world was shocked at the overwhelming and underestimated capacity of the Israeli military. The US immediately applauded and decided that "a logical corollary to our opposition to Arab nationalism should be to support Israel as the only pro-Western force left in the Middle East." And so US support for Israel skyrocketed and continued ever since, with Israel over the years serving its purpose and essentially becoming an offshore military base for the US.
By the early 1970's the US continued in its efforts to control the Middle East; preferring a hands off aproach where Israel, Turkey and Iran, armed with US weapons, would serve as "local cops on the beat" in Nixon's words. Egypt and Jordan were bought off as US client states and pledged not to fight with Israel in exchange for billions in annual bribes in agreement called the Camp David Peace Accords. The tiny Arab sheikdoms of the Persian Gulf were ruled by pro-US dictators. By the end of the decade, there were only a handful of states not under US control.
But suddenly the Shah of Iran was overthrown by his own people, who were quite angry with the United States, the US having 25 years earlier quite publically overthrown the elected govt of Iran and installed the Shah as a brutal but American friendly dictator. The new government of Iran pledged an Islamic revolution across the middle east, reminding the US of Nasser and everyone thinking "here we go again!"
So when the next year Iran went to war with its neighbor, Iraq, the US backed Iraq, watching with glee as 1 million died on each side. However after that war, Iraq complained that its neighbor Kuwait was exporting more oil then the OPEC quota allowed for, deflating world oil prices but also deflating a rather broke and indebted Iraqi treasury. After then accusing Kuwait of slant drilling across the border into an Iraqi oilfield, Iraq invaded and annexed Kuwait.
And then for the first time the US was involved in a real war in the middle east. Watching as the Soviet Union was crumbling and realizing that there was finally no deterent to US power, the Americans decided all focus should be on the middle east and sent half a million troops to drive Iraq out of Kuwait and reinstate the Kuwaiti dicator. Ten years later, the US decided Iraq would probably never become a US client state with the current regime, and invaded and occupied that country.
As of 2006, the United States had bases/military in the region included Bahrain, Qatar, the United Arab Emirates, Oman, Saudi Arabia, Yemen, Kuwait, Iraq, Turkey, Jordan, Israel, Egypt. The only ones without US military presence are Iran, Syria and Lebanon.
Iran is currently surrounded by the US military, with the US currently occupying Iraq to the west and Afghanistan to its right, US bases in Turkey, bordering north west Iran and a growing US military presence in the Caspian Sea region to its north, and the nuclear armed US Fifth fleet floating to its south. In the wake of US threats on Iran, it began enriching uranium as a part of a nuclear energy program, although some suspect it may be trying to develop a nuclear bomb to deter US attack, following the North Korean example. Iran insists it is enriching uranium for energy purposes, but will give it up in exchange for a promise by the US not to attack. The US currently refuses that promise, though recently said if Iran gives up its nuclear program, the US will grant Iran the priveledge of direct talks.
Syria also surrounded by the US military, is currently controlled by the secular/socialist Ba'athist party, led by dicatator Bashar al-Assad. It also faces routine threats from the US military, even after initially giving aid to the US in counter-terrorism operations.
Lebanon was never really a threat to US domination as a state, because the state itself was weak and helpless amid a diverse christian/muslim population. It fell into Civil War in the 1970's, with Syria invading in 1976 to protect its interests. It was also invaded by Israel in 1978 and 1982, who were attempting to crush the Palestinian Liberation Organization (which failed.) Syria occupied part of Lebanon until 2005, and Israel occupied part of Lebanon until 2000. Iran and Syria funded Lebanese who fought the Israeli occupation, which morphed into an entity called Hizbullah. Hizbullah became part terrorist organization, part community activist (providing social services for locals) and part political party, represented in Lebanon's parliament. When Israel withdrew from Lebanon in 2000, many Lebanese and Arabs throughout the world credited that to Hizbullah, and its stature rose in great pride as the only Arab force ever to successfully force an Israeli retreat; although the real reasons for the withdrawal were a bit more complicated.
Current Conflict: As of 2006, Hizbullah was one of the only forces in the region opposed to US dominance in the region that had any power. Most people in the region opposed US dominance, but they were living under US friendly dictatorships. The current US/Israeli siege on Lebanon is partially to destroy one of the last obstacles to complete US domination. I suspect the timing is related to the fact that Iraq has become a disaster with the only thing close to the government is run by pro-Iranian Shiites; which is causing a huge concern for the Sunni Arab states of the region (that hate Shiite muslims.) Thus it seemed like a good time to attack Hizbullah, which is an Iranian financed and Shiite, assuming most Arab states would support the attack, and they did (although because of the scale of destruction are now turning against it.) I also suspect the attacks serve to diminish leverage Iran has in the region, especially if the US has to have direct talks with Iran, and also to eliminate an obstacle to Israel finalizing its own borders, which according to its current PM requires stealing quite a large part of Palestinian land on the West Bank.
And thats a quick history of post-war US involvement in the Middle East!