Timeline: A century of changes in who can serve in the U.S. military

President Trump announced via Twitter on Wednesday morning that transgender people would no longer be allowed to serve in the U.S. military. That announcement came 69 years to the day after Harry Truman issued an order abolishing racial discrimination, and leading to the end of segregation, in the armed forces.

Here's how determinations of who is and isn't fit to serve have shifted over the past century:

• 1917-1918: During World War I, women are allowed to serve overseas only as nurses, telephone operators, administrators and secretaries.
• 1921: The U.S. Army says "stigmata of degeneration" such as "sexual perversion" or "feminine characteristics" can result in a male being labeled unfit for service.
• 1941: "Homosexual proclivities" are made a disqualifying condition for involvement in the military draft.
• 1948: President Truman signs the Women's Armed Services Integration Act, given women "regular and reserve status" in the Army, Navy, Air Force and Marine Corps.
• 1948: President Truman issues executive order 9981 which required equal treatment and opportunity for all service members regardless of race.
• 1949: Department of Defense releases memo saying homosexual individuals "should not be permitted to serve in any branch of the Armed Services in any capacity."
• 1981: Department of Defense releases Directive 1332.14, which labels "homosexual conduct" as "grounds for separation" from the military.
• 1993: President Clinton signs off on the Don't Ask, Don't Tell policy, which bans openly gay men, lesbians and bisexuals from serving.

• 2011: President Obama repeals Don't Ask, Don't Tell.
• 2015: Defense Secretary Ashton Carter says women will be "able to serve as Army Rangers and Green Berets, Navy SEALs, Marine Corps infantry, Air Force parajumpers and everything else that was previously open only to men."
• 2016: Secretary Carter declares that "effective immediately, transgender Americans may serve openly," lifting the Pentagon's previous ban on openly transgender service members.
• 2017: President Trump tweets that "the United States Government will not accept or allow Transgender individuals to serve in any capacity in the U.S. Military."