They were both ruled by the Liberal Party from the beginning. However, the Liberals were defeated in Alberta in 1921 by the United Farmers of Alberta (UFA) and have never been returned to power, although they have been the official opposition many times since then. In Saskatchewan, the Liberals remained in power from 1905 until 1944, although they needed to form a coalition with the Conservatives from 1929 to 1934 as neither party won a majority in the 1929 election.
The Social Credit defeated the UFA in the 1935 election and remained in power for 36 years, until 1971. In the late 1960's, the Social Credit, although still in power, had begun to lose popularity to the Progressive Conservatives. In an attempt to shore up their own fortunes, the Liberals and the Social Credit formed an electoral arrangement. However, they were both soundly defeated by the Progressive Conservatives in the 1971 election. As a result of this, the Liberal Party was nearly wiped out in Alberta. The Progressive Conservatives have now been in power in Alberta ever since 1971, having won the last 12 general elections. The Liberals regained much of their former status, forming the Official Opposition from 1993 to 2012, before losing that position to the Wildrose Party in the 2012 election.
As can be seen from the above, Albertans tend to re-elect one party consistently over protracted periods. The Liberals won the first 4 provincial elections, the UFA the next 3, followed by 9 wins by the Social Credit and the Progressive Conservatives have won the last 12 elections. In the beginning, this was also the case in Saskatchewan, with the Liberals winning the first 9 provincial elections and remaining in power from 1905 until losing to the Co-operative Commonwealth Federation (CCF) in the 1944 election. The CCF then won 5 consecutive elections, before the Liberals returned to power from 1964 to 1971. The New Democratic Party (NDP), formerly the CCF, won the 1971 election and the Liberals have not returned to power in Saskatchewan since that time. In fact, in the last 3 provincial elections, in 2003, 2007 and 2011, they have failed to win a single seat in the legislature.
From a position of strength in 1905, the Liberal Party has dwindled, in both Alberta and Saskatchewan, to where they are not currently even a major force. Current polls indicate they are favored by fewer than 10% of the populace in both provinces.