Iraq's 29 million inhabitants are mostly Muslim. They are divided along both religious (Shia and Sunni) and ethnic (Arab and Kurdish) lines. Under Saddam Hussein, the Sunni Arab minority dominated political and economic life.
As Shia leaders gained power in the wake of the invasion, many Sunnis boycotted the political process.
The Sunni vote grew in national elections in December 2005, however, and Shia parties fell short of an absolute parliamentary majority. After months of deadlock, Shia politician Nouri Maliki was appointed prime minister.
The Kurds live mainly in the north where they are largely autonomous.
Hundreds of thousands of people have been displaced within Iraq. Figures range from 300,000 to 1.9 million.