What is an example of how the principle "All Men Are Created Equal" has affected government policies in the modern era since 1945?
Each of these have effected change in the United States with regard to the principle all men are created equal...(and women) after 1945:
Brown v. the Board of Education 1954
Little Rock Crisis 1957
The Equal Pay Act 1963
Gideon v. Wainwright 1963
Miranda v. Arizona 1966
Civil Rights Act 1964
Voting Rights Act 1965
The Elementary and Secondary Education Act 1965-additional provisions
The Indian Self-Determination and Education Assistance Act 1975-additional provisions
The Americans With Disabilities Act 1990-additional provisions
One of the most significant times in 20th century America was the Civil Rights Movement of the 1960s when equality was the goal of all oppressed people; namely women and African-Americans. This movement coincided with the opposition to the war in Vietnam and followed the overzealous and often unjustified condemnation of political dissidents (particularly communists) by Josephy McCarthy in the preceding decade. So, this moment in America’s history was built on peaceful (MLK) and sometimes violent (Malcolm X) protests against the war and against oppression, segregation and prejudice in America. “All men are created equal” was invoked frequently during this time, most famously in Martin Luther King’s “I Have a Dream” speech, which may be the most famous speech of the movement and of the last half century. The speech and the Civil Rights Movement as a whole was responsible for ongoing political discussion, openness about race relation and the need to fully realize the tenets of freedom and equality versed in the Constitution. The Civil Rights Movement eventually led to multiple legislations. The Civil Rights Act of 1964 outlawed segregation in schools, extended voting rights and protection to black voters and outlawed discrimination in work and public facilities.
If you are asking about government policies in the United States, then the most obvious answer would be that this principle has affected government policies towards racial minorities. Since the Civil Rights Movement, many government policies have been aimed at trying to ensure that people should have equal rights.
Before the Civil Rights Movement, of course, black people were not treated as if they were created equal. This was the law in many states. But then, the Brown v. Board of Education case laid out a ruling based on the principle that all people are created equal and must be allowed to go to school together. Similarly, the Civil Rights Act of 1964 was meant to ensure that people would be treated equally.
So, the move from a society that was racially segregated by law to one that was not is an example of how this principle has affected government policies since 1945.