was the first party involved in civil war?
Yes, Spanish Civil War
Spanish Socialist Workers' Party
The PSOE played a key role during the Second Spanish Republic, being part of coalition government from 1931 to 1933 and from 1936 to 1939, when the Republic was defeated by Francisco Franco in the Spanish Civil War. 
who were the major candidates in 1936 spanish general election? Popular Front and Spanish Confederation of the Autonomous Right (CEDA) did anything noteworthy happen before it? In the 1933 election, Spain was divided into multi-member constituencies. what was the result of the election? The winners of the 1936 elections were the Popular Front. which parties were a part of the popular front? Spanish Socialist Workers' Party (PSOE), Republican Left (Spain) (IR), Esquerra Republicana de Catalunya (ERC), Republican Union (UR), Communist Party of Spain (PCE), Acció Catalana (AC) and other parties.
wiki:19928037
Spanish Socialist Workers' Party [SEP] Introduction
Historically a Marxist party, it abandoned Marxism in 1979. The PSOE has historically had strong ties with the General Union of Workers (UGT), a Spanish trade union. For a couple of decades, the UGT membership was a requirement for the PSOE membership. Since the 1980s, the UGT has frequently criticized the economic policies of the PSOE, even calling for several general strikes against the PSOE governments on 14 December 1988, 28 May 1992, 27 January 1994 and 29 September 2010, all jointly with the Workers' Commissions, another major trade union. Both the trade unions and the left have often criticized the economic policies of the PSOE for its economic liberal nature, have denounced the policies of deregulation and generalization of the precarious and temporary work, cuts in social benefits such as unemployment and retirement as well as the privatisations of big companies and public services.