Trump's war on terror will mostly change from Bush's war on terror and Obama's war on terror. I'm guessing he will ask the CIA to financially disclose who finances the radicals in Islam, and find dozens of folders sitting there with details leading back to Saudi individuals.
In a matter of weeks, I think each of those will find their US visas no longer valid. The Saudi government will jump right in and haul up their usual Senator group to complain.....with Trump just grinning. Trump might even go and ID each Senator on the payroll of Saudi backers.
Legal paperwork will likely be fixed to freeze individual accounts throughout the US and Europe, and a year from now....around two or three dozen Saudi backers of radical Islam will be roped off and identified in public news media.
The drone war? It might continue in Syria and Iraq....but I think it'll basically end throughout the rest of the world.