Jamieson, Fausset and Brown on Daniel 2:35

35. broken ... together--excluding a contemporaneous existence of the kingdom of the world and the kingdom of God (in its manifested, as distinguished from its spiritual, phase). The latter is not gradually to wear away the former, but to destroy it at once, and utterly (2Th 1:7-10; 2:8). However, the Hebrew may be translated, "in one discriminate mass."

chaff--image of the ungodly, as they shall be dealt with in the judgment (Psa 1:4, 5; Mt 3:12).

summer threshing-floors--Grain was winnowed in the East on an elevated space in the open air, by throwing the grain into the air with a shovel, so that the wind might clear away the chaff.

no place ... found for them--(Re 20:11; compare Psa 37:10, 36; 103:16).

became ... mountain--cut out of the mountain (Da 2:45) originally, it ends in becoming a mountain. So the kingdom of God, coming from heaven originally, ends in heaven being established on earth (Re 21:1-3).

filled ... earth--(Is 11:9; Ha 2:14). It is to do so in connection with Jerusalem as the mother Church (Psa 80:9; Is 2:2, 3).