Here we go again.

Three years after U.S. combat troops left Iraq, the political situation is turning red hot, and a radical group is closing in on Baghdad.

The Islamic State of Iraq and Syria (ISIS), is creating chaos across the middle eastern country. All or parts of several major Iraqi cities are already under control of violent extremists.

Iraq was already a dangerous and unstable place before ISIS launched its offensive about six months ago. More than 8,000 Iraqi civilians were killed by sectarian fighting in 2013. The country’s ruling government is way too cozy with Iran, the region’s largest supporter of terrorism.

How did they get here?

Iraq’s Shiite-dominated government, led by Prime Minister Nouri al-Maliki, has done little to reconcile with other religious and ethnic groups in Iraq, notably Sunnis, who are a minority. Sunni insurgents have fed on that Sunni fear and discontent to draw recruits and support its cause.

Iraq’s army, once a symbol of national power, is viewed y many in Iraq as just another militia designed to protect the regime, not the nation. Built with billions of dollars of U.S. taxpayer money, Iraq’s army collapsed in the face of the insurgent threat.

In the early 1990s, Saddam Hussein was swiftly punished for invading Kuwait and threatening Saudi Arabia. Iraq and Saddam were mostly contained, in an arrangement that, while not perfect, was preferred to a costly war.

Then post-9/11, the Bush administration promoted the theory that toppling Saddam and installing a democracy in Iraq would produce a more peaceful Middle East. The results are before us.

The verdict on the Bush administration’s role in this fiasco is already in. It failed. The lesson for presidential administrations and members of Congress — both current and future — is to apply U.S. military firepower with more care.