Final answer:
The last invasion of Iran occurred during the Iraq-Iran War from 1980 to 1988 led by Iraq's Saddam Hussein. The invasion was motivated by territorial disputes and religious and ethnic differences between Iran and Iraq.
Step-by-step explanation:
The last invasion of Iran occurred during the Iraq-Iran War that started in September 1980 and lasted until an armistice in 1988. The invasion was carried out by Iraq, led by Saddam Hussein. The main reason behind the invasion was a combination of territorial disputes and religious and ethnic differences between Iran and Iraq. The conflict began with a disagreement over the Shatt al-Arab waterway and was fueled by the ethnic and religious tensions between the predominantly Shia Muslim Iranians and the Sunni Muslims of Iraq.