Historically, the party belonged to the wing of international communism that looked to the Soviet Union for inspiration. In the mid-1960s, the U.S. State Department estimated the party membership to be approximately 100. The party grew consistently through the 1960s and 1970s. In the late 1960s, some IWP members (notably Michael O'Riordan) became active in the Dublin Housing Action Committee. The IWP also condemned the Soviet Invasion of Czechoslovakia, although O'Riordan was opposed to this position. In March 1970, following the CPNI/IWP merger, the new Communist Party of Ireland issued a manifesto called "For Unity and Socialism", advocating the election of left-wing governments in both parts of Ireland, and, eventually, the creation of a United Ireland.