I think it's safe to say that all the world wanted was for America to get out of the Middle East, a region destabilized by foreign interference and countless disputes over land and religion. Politics in the Middle East has always been tricky, with an element of religion and ethnicity underlying motives. However, the support from America for the Kurdish people in Syria has been a constant effort to prevent genocide, and support the imprisonment of ISIS rebels.
Now that Trump has withdrawn U.S. support, the Kurdish people have no one to protect them from Trukish forces. The Turkish forces have begun attacking and killing Kurds, a minority group of Muslims who are native to the Mesopotamian region. They once had a nation called Kurdistan that was disbanded during the Treaty of Lausanne which established modern day Turkey.
Now, what does this mean for the Muslim world?
The Muslim world never asked for the western Allies after World War One to randomly draw state lines of their former colonies. The Muslim world never asked the west to invade and "investigate" their resources. The Muslim world never asked the west to sell armed weapons to rebel groups. Yet, when the U.S. was in charge of stabilizing the region, they gave their word. For a country known as perhaps the strongest and most economically successful nation in the world, their word means everything -- and the whole world watches if they keep it.
Therefore, backing out on a promise has immense consequences for the U.S. on the world stage, and leaves the Middle East vulnerable to a fight for power. The Kurds are left to fend for themselves amongst huge powers like Turkey and Iran -- all in the chaos of Syria.
What does this say about America's moral code?
America's word is no longer trustworthy, and the Muslim world will most likely never trust the U.S. again.