What observations helped Hubble to conclude that the universe is expanding?

Hubble observed that distant galaxies were moving away from Earth, which he noted through the redshift of their light spectra. This redshift indicated that the wavelengths of light were stretched, implying these galaxies were receding from us. Hubble also found a linear relationship between the distance of galaxies and their recessional velocity, leading to the conclusion that the universe is expanding uniformly in all directions. This pivotal discovery became known as Hubble's Law.