Ahmad al-Jarba is president of the National Coalition of Syrian Revolution and Opposition Forces. Brig. Gen. Salim Idris is chief of staff of the Supreme Military Council of the Free Syrian Army.

Of all the popular uprisings in recent history, that of the Syrian people is the most documented. For 2 1 / 2 years, the Assad regime’s inhumane military repression has been shown to the world through testimonies, photos and video footage captured on the mobile phones of terrified Syrians and, increasingly, through reports from respected international journalists.

It has never been more important to remember that the first months of the revolution resonated with the heartfelt slogans of “The Syrian people are one” and “Peaceful.” Even when Bashar al-Assad’s security forces upgraded their repression from live fire to airstrikes, peaceful demonstrators continued to chant, armed with banners, flowers and even cool water for the very security forces tasked with crushing them. For daring to be one of the leaders of such an inspiring, nonviolent civil movement, 26-year-old Ghiath Matar was arrested in Daraya in September 2011, tortured and killed. He became one of the early symbols of the Syrian revolution.

Assad’s calculated, cold-blooded brutality pushed Syrians into self-defense and armed resistance. Had thousands of brave soldiers not defied the regime’s orders to kill demonstrators and defected to form the Free Syrian Army — joined gradually by civilians defending their families — Assad’s incredible violence would have continued unopposed, as the repression has elicited general indifference from the international community.

This international apathy and indecision convinces Assad that he is invincible and emboldens him to unleash barbaric horrors on a defenseless population. Assad’s deadliest chemicals were released Aug. 21 in areas of Damascus, killing more than 400 children and some 1,000 adults. This was not the first time Assad has used chemical weapons on his people, and it won’t be the last if he is not stopped.

Numerous warnings have passed unheeded. In February, the U.N. High Commissioner for Human Rights, Navi Pillay, repeated her call — first made in December 2011 — for Assad to be referred to the International Criminal Court for crimes against humanity. Meanwhile, the U.N. High Commissioner for Refu­gees, António Guterres, is pleading with the international community: “Syria has become the great tragedy of this century, a disgraceful humanitarian calamity with suffering and displacement unparalleled in recent history,” he said last week.

For all its horror, the situation today is minor compared with what could still happen if Assad is not deterred or held accountable for his crimes. It took one year for the first million Syrians to seek refuge in neighboring countries but only six months for the second million to escape Assad’s brutality; what mass exodus will follow if he gets away with his chemical massacres? At least a third of Syria’s population is homeless and destitute; inaction will augment the scale of this unprecedented humanitarian catastrophe, and despair will breed radicalism — especially if more chemical attacks are carried out.

History shows that Assad understands only green lights or red lights — nothing in between. So far, global inaction and his allies’ protective actions have granted him impunity to terrorize his nation and the region. Dithering by the world’s most powerful states empowers not only the vicious Assad regime but also the extremist agenda of the al-Qaeda-style terrorists seeping into Syria from the east. They are fighting not only Assad but, more important, also those who oppose Assad.

The longer Assad’s reign continues out of control, the more extremists will exploit the situation and the less stable the entire region will become.

The Syrian Coalition has been recognized as the legitimate representative of the Syrian people by more than 100 countries, including the United States. It is in this capacity that we ask Congress and the American people to restrain Assad’s destructive capacities. Please authorize President Obama to act against Assad and to stop him in his deadly tracks.

With the death toll well past 100,000, our struggle to liberate our country from this murderous regime and to protect our people continues, but only the United States can deter Assad from using his chemical weapons again. The lives of millions of Syrians, and the safety of the region, are at stake.