Indians lent their support enthusiastically in World War I to Great Britain, thinking that it would help them become equal partners in the British Empire. A brief take on this can be found here. Even the pacifist Mahatma Gandhi said "I would make India offer all her able-bodied sons as a sacrifice to the Empire at this critical moment, and I know that India, by this very act, would become the most favored partner in the Empire, and racial distinctions would become a thing of the past." [1] 800,000 Indians saw combat, 1.5 million volunteered. But, as the aforementioned link will tell you:
And in 1919, there was the Jallianwalla Bagh massacre.
Meanwhile, in the US of A, events were proceeding in parallel. C. Vann Woodward [2] tells us what happened following World War I.
The Empires made promises they had no intention of keeping.
[1] Robert Payne, The Life and Death of Mahatma Gandhi, pg 327.
[2] C. Vann Woodward, The Strange Career of Jim Crow, third edition, pg 114-115.
The British government’s post-war attitude quickly alienated Ghandi and was a great stimulus for his independence movement.
And in 1919, there was the Jallianwalla Bagh massacre.
Meanwhile, in the US of A, events were proceeding in parallel. C. Vann Woodward [2] tells us what happened following World War I.
The war aroused in the Negroes a new hope for restoration of their rights and a new militancy in demanding first-class citizenship. More than 360,000 of them entered military service and a large part of those saw overseas duty in uniform. More joined the exodus of migration to the North in quest of high wages in the war industries. Temporary prosperity gave them new hopes and desires that needed fulfillment, and official propaganda picturing American participation in the war as a crusade for democracy raised the natural demand for a little more democracy at home.
The war-bred hopes of the Negro for first-class citizenship were quickly smashed in a reaction of violence that was probably unprecedented. Some twenty-five race riots were touched off in American cities during the last six months of 1919, months that John Hope Franklin called 'the greatest period of interracial strife the nation has ever witnessed." Mobs took over cities for days at a time, flogging, burning, shooting and torturing at will. When the Negroes showed a new disposition to fight and defend themselves, violence increased. Some of these atrocities occurred in the South—at Longview, Texas, for example, or at Tulsa, Oklahoma, at Elaine, Arkansas, or Knoxville, Tennessee. But they were limited to no one section of the country. Many of them occurred in the North and the worst of all in Chicago. During the first year following the war more than seventy Negroes were lynched, several of them veterans still in uniform.
The Empires made promises they had no intention of keeping.
[1] Robert Payne, The Life and Death of Mahatma Gandhi, pg 327.
[2] C. Vann Woodward, The Strange Career of Jim Crow, third edition, pg 114-115.
PS, remembering the 1919 race riots in Washington, DC, the Washington Post has this (emphasis added)
Racial resentment was particularly intense among Washington's several thousand returning black war veterans. They had proudly served their country in such units as the District's 1st Separate Battalion, part of the segregated Army force that fought in France. These men had been forced to fight for the right to serve in combat because the Army at first refused to draft blacks for any role other than laborer. They returned home hopeful that their military service would earn them fair treatment.
Instead, they saw race relations worsening in an administration dominated by conservative Southern whites brought here by Woodrow Wilson, a Virginian. Wilson's promise of a "New Freedom" had won him more black voters than any Democrat before him, but they were cruelly disappointed: Previously integrated departments such as the Post Office and the Treasury had now set up "Jim Crow corners" with separate washrooms and lunchrooms for "colored only." Meanwhile, the Ku Klux Klan was being revived in Maryland and Virginia, as racial hatred burst forth with the resurgence of lynching of black men and women around the country – 28 public lynchings in the first six months of 1919 alone, including seven black veterans killed while still wearing their Army uniforms.