Datan and Aviram, members of the tribe of Reuben, were among the first to join Korah in his rebellion against Moses. The Sages explain that the physical proximity between the location of the tribe of Reuben and Korah’s family caused them to follow in Korah’s path.

“And Datan and Aviram” (Numbers 16:1). From here the Sages said: Woe unto the wicked and woe unto his neighbor. Datan and Aviram joined Korah first because they were neighbors of Korah, whose family encamped to the south of the Tabernacle, as it is written: “The families of the sons of Kehat shall encamp on the side of the Tabernacle to the south” (3:29). And the camp of Reuben was adjacent to them, as it is stated: “The banner of the camp of Reuben is to the south according to their hosts” (2:10)…and Datan and Aviram, who were neighbors of the disputant, were stricken with him and were eliminated from the world. (Bemidbar Rabba 18)