The 20th century brought with it a musical style that was hard to really define. It was irregular and constantly changing and most of the time quite unsettling. This was largely due to the dissonant harmonies and a 12-tone chromatic scale. It relied more on rhythm than harmony.
With this in mind, the trumpet played an important role as a star solo in orchestral compositions because of its tonality. The trumpet fit perfectly into the 20th century style that was largely influenced by France.
As the 20th century progressed, Jazz came about that was largely influenced by the trumpet. The trumpet and Jazz started picking up momentum in the southern United States and then slowly became more popular. In the latter half of the 20th century, rock became an important musical staple but it did not include the trumpet which had previously played such a large role.