This is an ancient phenomena. When new lands are opened up for settlement, farms are all owned by individual families. But some farmers are more efficient than others and amass more wealth in the form of surplus crops, livestock or money. In bad crop year, the less efficient farmers have to sell some of their land to the more successful farmers to survive. The more efficient farmers increase the size of their holdings over the generations. This is what happened in Rome, after many farmers first got their own farms on land conquered from neighbors. The rich got richer and the poor became landless members of the city "mob" or turned into serfs.