Founded in 1919 as a successor to Poalei Zion, Ahdut Ha'avodah (Unity of Labor) merged with HaPoel HaTzair, in 1930, and formed Mapai. In 1944, Siah Bet, a faction that split from Mapai, used Ahduts name and formed a new political party with HaKibbutz HaMeuhad (United Kibbutz Movement). In 1954, Ahdut HaAvodah was reconstituted again when some members left Mapam and joined with members of HaKibbutz HaMeuhad. From 1965 to 1968, Ahdut aligned itself with Mapai and was finally absorbed by the Labor Party.
Sources: "Political Parties and Organizations." Appendix B