Why is a dominant chord important in a key signature?

A dominant chord plays a crucial role in tonal music because it creates a strong sense of tension that seeks resolution back to the tonic chord. This relationship is foundational in Western tonal harmony; the dominant chord, typically built on the fifth scale degree, contains notes that naturally lead back to the tonic. The seventh in the dominant chord, for instance, is a leading tone to the tonic, which enhances the drive toward resolution. This progression from the dominant back to the tonic is not only fundamental to establishing key relationships but also underpins countless musical structures, creating a satisfying closure or cadence in compositions. Thus, the importance of the dominant chord lies in its function as a pivotal element in the harmonic progression, reinforcing the tonal framework and providing a sense of directionality in music.