It is becoming increasingly likely that eventually either the government of the United States or the government of Israel will launch an attack against Iran. The current support for the Syrian rebels by President Obama is to undermine a mutual defense treaty between the governments of Syria and Iran that if either is attacked by the United States the other would respond. If the rebels take control of Syria, that isolates Iran from one more ally.
But if either the United States or Israel attacks Iran, not only will the other country be brought into the conflict, many other countries are poised to be brought into the conflict as well. The support that the government of the United States shows for the government of Israel has been a source of discontent in many other Middle Eastern countries.
If Israel attacks Iran, it would be with the understanding that the United States will support Israel against a counter-attack, thus proving the dangers of entangling alliances once again. As the Iranian military launches what counter-attacks they are capable of, the government of Israel will be calling upon the United States to save Israel from destruction.
If the United States launches an attack against Iran, Israel will likely be drawn in by popular sentiment among the peoples and government of the other countries in the area. Popular support no longer exists for the United States in most countries, and the various "Arab Spring" revolutions have not brought to power governments friendly to the United States. It would not be hard to imagine these new post-revolution countries retaliating against Israel for an attack by the United States against Iran.
A general war against many Middle-East countries is not the worst scenario though. The whole situation can get very bad very quickly if the governments of Russia and China get tired of provocations by the United States and come to the aid of Iran. The government of Iran has been carefully cultivating ties with both of those countries, and China in particular is very interested in more sources of petroleum.
It could start like Vietnam, with the armies of various countries supporting one side and armies of various countries supporting the other side. It would be a terrible war for the Persian people, with United States troops fighting Russian and Chinese troops on Persian soil, but there is no need to believe that the war would be maintained there.
With the United States so heavily engaged in Iran, the government of Pakistan would finally see an opportunity to act against the United States in retaliation from drone bombings. Working with the people of Afghanistan, the Pakistani military would also come to the support of Iran. China and Pakistan have been cultivating closer ties in an effort to put pressure on a mutual rival of India.
A general Muslim uprising coupled with Russian and Chinese support would force the call-up of the NATO allies. Britain would already be heavily involved because the United States is involved, but this would mobilize the militaries of several other countries, especially former Warsaw Pact members. In 2008 the government of Georgia tried to pull the United States into a conflict with Russia over the Georgian province of South Ossetia. The government of Russia saw the admittance of former Warsaw Pact and former Soviet Socialist Republics into NATO as a provocational encroachment.
Although the war would not be directly between NATO and Russia, the war would be directly between Europe and the Middle East. Many European countries are already experiencing difficulty assimilating immigrants, although it is politically incorrect to discuss the subject. These people would be easily made into scapegoats for the problems in various European countries, from Algerians in France to Pakistanis in England to Turks in Germany. A similar conflict might also occur in Australia.
The country with the most to lose at this point is Turkey. Straddling the border of Europe and the Middle East as it does, being a predominantly Muslim country with a secular government, already a NATO member and trying to gain entry into the European Union, a war between Europe and the Middle East spells disaster for Turkey no matter which side is chosen. Relations between Turkey and Israel have cooled significantly over the Gaza flotilla issue. While Turkey wouldn’t mind a weakened Iran, giving Turkey more influence in the Middle East, it is questionable if the population would support Turkey siding with Europe. Siding with the Middle East, on the other hand, would be in violation of both treaties and political objectives.
Finally, in the worst case scenario, tension between Pakistan and China on one side and India on the other brings India into the conflict on the side of the United States. Although that would be a great relief to the United States considering the population of India rivals that of China, it would in the long run only make the war worse for everyone. Plus North Korea might try to take advantage of the confusion to attack South Korea, although that would not work very well for North Korea. It could draw the United States into another front, fighting North Koreans and Chinese on the east side of Asia.
With the United States, Israel, India, and NATO on one side, and China, Iran, Russia, and the Middle East on the other, this would be a devastating war. So devastating, in fact, that it is surprising that politicians in office today are still calling for action against Iran. This is not the only possible outcome, and might not even be the most likely outcome, but World War One was started by a complicated series of entangling alliances as well.