FILE PHOTO: U.S. Defense Secretary James Mattis listens as U.S. President Donald Trump (not pictured) speaks to the news media while gathering for a briefing from his senior military leaders in the Cabinet Room at the White House in Washington, U.S., October 23, 2018. REUTERS/Leah Millis/File Photo

WASHINGTON (Reuters) - U.S. Defense Secretary James Mattis resigned on Thursday, effective Feb. 28, 2019, over disagreements in policy following President Donald Trump’s recently announced decision to withdraw U.S. troops from Syria.

The following are the key highlights from his resignation letter:

“One core belief I have always held is that our strength as a nation is inextricably linked to the strength of our unique and comprehensive system of alliances and partnerships. While the US remains the indispensable nation in the free world, we cannot protect our interests or serve that role effectively without maintaining strong alliances and showing respect to those allies.”

“Like you, I have said from the beginning that the armed forces of the United States should not be the policeman of the world. Instead, we must use all tools of American power to provide for the common defense, including providing effective leadership to our alliances. NATO’s 29 democracies demonstrated that strength in their commitment to fighting alongside us following the 9-11 attack on America. The Defeat-ISIS coalition of 74 nations is further proof.”

“I believe we must be resolute and unambiguous in our approach to those countries whose strategic interests are increasingly in tension with ours.”

“It is clear that China and Russia, for example, want to shape a world consistent with their authoritarian model – gaining veto authority over other nations’ economic, diplomatic, and security decisions – to promote their own interests at the expense of their neighbors, America and our allies.”

“My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues. We must do everything possible to advance an international order that is most conducive to our security, prosperity and values, and we are strengthened in this effort by the solidarity of our alliances.”

“Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position.”