All over the world, millions of innocent people are facing persecution, imprisonment, and even death because of their religious beliefs. In 2013, the world witnessed the largest displacement of religious communities in recent memory, according to the State Department's Annual Report on International Religious Freedom. And the trend in 2014 is only getting worse. But perhaps nowhere has intolerance, ruthlessness, and evil combined to destroy people of faith more than it has in Iraq, where the Islamic State is engaged in a systemic effort to wipe out the Christian presence there, along with all other religious minorities. The Islamic State, an extreme Sunni militant group that emerged from al-Qaeda, has rampaged across Iraq, ridding towns of Christians and other religious minorities, just as it did in parts of Syria over the last year, persecuting that country's Christians. It has used brutal tactics such as beheadings, rapes, forced conversions, and forced marriages of any non-Sunnis in its path. The United States intervened militarily to assist 40,000 Iraqi Yazidis -- a religion that fuses Christianity, Islam, and ancient Zoroastrianism -- who were literally stuck on a mountaintop. Until U.S. and Kurdish military operations helped clear a path to safety, their options were to stay and die of thirst, or relocate and be massacred by the Islamic State militants waiting at the base of the mountain. The U.S. government took the correct action in halting the genocidal campaign of the Islamic State by using our military to perform limited air strikes against their positions that were threatening Mount Sinjar and by conducting humanitarian airdrops to the Yazidis who were facing death from lack of water. Although the Obama administration has indicated that the mission has been accomplished on Mount Sinjar, there are reports that thousands of Yazidis still remain in peril on the mountain, in addition to the hundreds of thousands of refugees who need of humanitarian assistance in the Kurdish region of Iraq. Although the Mount Sinjar crisis further revealed to the world the sheer brutality of the Islamic State, for months these terrorists have been occupying and destroying churches across Iraq, pulling down crosses, destroying religious documents and holy sites, and forcing Christians to convert or face death. They have seized bridges, dams, and other infrastructure that Christian towns and communities rely on for survival. Christians have been the primary target in Iraq, raising the stakes and the need for U.S. leadership. Christians have inhabited Iraq and Syria for 2,000 years; but if the Islamic State has its way with its "convert or die" tactics, not a single Christian will be left. But it is important not to lose sight of the fact that it is not just the fate of Christians and other religious minorities at stake in Iraq and Syria. Allowing the Islamic State and its jihadist leaders to maintain their newly established caliphate in the heart of the Middle East is a national-security threat to the United States and to our allies in the region. We need to be doing much more to address this challenge, including air strikes against Islamic State targets and increased lethal assistance to the Kurds and Iraq's central government. The Kurds in particular are hosting more than a million refugees from other parts of Iraq and Syria who have fled their villages as the jihadists have advanced. They are short on funds and resources because of ongoing disputes with the government in Baghdad, and we need to be more responsive to their requests for direct financial and military aid. In Iraq and around the world, protecting religious freedom must be a top priority of our foreign-policy agenda. One need look no further than the situation we face in Iraq and Syria today to realize that, if left unchecked, the same forces that breed anti-religious extremism will eventually affect our security here at home.

Marco Rubio represents Florida in the U.S. Senate and is a member of the Senate Foreign Relations Committee and Senate Select Intelligence Committee.