Complex sentence: Traditionally, cadences act both harmonically, to establish tonal centers, and formally, to articulate the end of sections; just as the tonic triad is harmonically central, a dominant-tonic cadence will be structurally central.
Split into simpler sentences: Traditionally, cadences act both harmonically, to establish tonal centers, and formally, to articulate the end of sections. Just as the tonic triad is harmonically central, a dominant-tonic cadence will be structurally central.