Shortly after President Trump announced he planned to bring American troops home from Syria there was suddenly another chemical weapon attack. There is no logical reason for President Assad to stir up things in this way because he can only gain with US withdrawal. Was this another false flag operation by US intelligence or other dark forces to prevent peaceful withdrawal of US military?

Both the chemical attacks done under Assad's regime, the one shortly after Trump was sworn in and the recent one, were orchestrated by US intelligence agencies so that the plight of the innocent civilians in harm's way could be broadcast widely and then used as a justification for reprisal and a rationale to keep the United States engaged in the region militarily. The purpose is exactly as you saw intuitively, to create the semblance of wanting to be nice and to limit US involvement in military action beyond absolute necessity, but then on the brink of bringing home the troops, an event happens showing this is unwise and there must, in fact, be a ramping up of military action to punish this travesty and prevent it from happening. So this is done for political purposes as well as furthering the cause of Extraterrestrial Alliance to hamper, hinder, and weaken humanity.