What critical concept did Hubble secure by successfully bridging the distance measurement gap between our local stars and intergalactic space?

Answer

The cosmic distance ladder

Hubble's success in measuring the distance to M31 provided the crucial first rung upon which the cosmic distance ladder, used to measure all astronomical scales, is built.

What critical concept did Hubble secure by successfully bridging the distance measurement gap between our local stars and intergalactic space?
measurementgalaxyAstronomerDistancecalculation