H.R. McMaster has served his country with distinction for more than 30 years. He has won many battles, and his bravery and toughness are legendary. General McMaster's leadership of the National Security Council staff has helped my administration accomplish great things to bolster America's national security. He helped develop our "America first" National Security Strategy, revitalize our alliances in the Middle East, smash ISIS, bring North Korea to the table, and strengthen our Nation's prosperity. This work and those achievements will ensure that America builds on its economic and military advantages. I thank General McMaster and his family for their service and wish them the very best.
NOTE: The statement referred to the Islamic State of Iraq and Syria (ISIS) terrorist organization.
Donald J. Trump (1st Term), Statement on the Resignation of National Security Adviser H.R. McMaster Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/332936