The Catholic teaching on the Assumption of Mary was defined as dogma by Pope Pius XII on November 1, 1950, through the apostolic constitution "Munificentissimus Deus." This declaration affirmed that Mary, the mother of Jesus, was assumed body and soul into heavenly glory at the end of her earthly life.

The decision to define the Assumption as dogma stemmed from several factors:

1. Historical Belief: The belief in the Assumption of Mary had been part of the Church's tradition since the early centuries. Many Christian communities celebrated the feast of the Assumption long before it was officially defined.

2. Theological Development: The 19th and early 20th centuries saw a growing interest in Marian doctrines. As a result, theologians and the faithful increasingly sought formal recognition of the Assumption.

3. Ecumenical Context: The move to define the dogma was also influenced by the desire to affirm the role of Mary in salvation history and to strengthen the Church’s identity in a time of growing secularism and diverse religious beliefs.

4. Papal Authority: Pope Pius XII’s declaration emphasized the authority of the papacy in defining matters of faith and morals, further solidifying the Church's teachings on Mary.

The official definition of the Assumption as dogma affirmed the belief that Mary, having completed her earthly life, was taken up into heaven, reflecting her unique role in God's plan of salvation. This dogma serves to highlight the dignity of Mary and her closeness to her Son, Jesus Christ.

For more detailed information, you can refer to the full text of "Munificentissimus Deus" here.