Well, that's a difficult thing to do, but here's an article:
By 1968 the López Arellano regime seemed to be in serious trouble. The economic situation was producing growing labor conflicts, political unrest, and even criticism from conservative groups such as Fenagh. Municipal elections were held in March 1968 to the accompaniment of violence and charges of open fraud, producing PNH victories but also fueling public discontent and raising the concern of the United States Embassy. Efforts at opening up a dialogue were made in mid-1968 but had little success. Later in the year a general strike was kept brief by government action that helped break the strike and exiled the leader of the major Caribbean coast labor federation. Unrest continued, however; in the spring of 1969 new strikes broke out among teachers and other groups.
As the political situation deteriorated, the Honduran government and some private groups came increasingly to place blame for the nation's economic problems on the approximately 300,000 undocumented Salvadoran immigrants in Honduras. Fenagh began to associate Salvadoran immigrants with illegal land invasions, and in January 1969, the Honduran government refused to renew the 1967 Bilateral Treaty on Immigration with El Salvador that had been designed to regulate the flow of individuals across their common border. In April INA announced that it would begin to expel from their lands those who had acquired property under agrarian reform without fulfilling the legal requirement that they be Honduran by birth. Attacks were also launched in the media on the impact of Salvadoran immigrant labor on unemployment and wages on the Caribbean coast. By late May, Salvadorans began to stream out of Honduras back to an overpopulated El Salvador.
Tensions continued to mount during June 1969. The soccer teams of the two nations were engaged that month in a three-game elimination match as a preliminary to the World Cup. Disturbances broke out during the first game in Tegucigalpa, but the situation got considerably worse during the second match in San Salvador. Honduran fans were roughed up, the Honduran flag and national anthem were insulted, and the emotions of both nations became considerably agitated. Actions against Salvadoran residents in Honduras, including several vice consuls, became increasingly violent. An unknown number of Salvadorans were killed or brutalized, and tens of thousands began fleeing the country. The press of both nations contributed to a growing climate of near- hysteria, and on June 27, 1969, Honduras broke diplomatic relations with El Salvador.
Early on the morning of July 14, 1969, concerted military action began in what came to be known as the Soccer War. The Salvadoran air force attacked targets inside Honduras and the Salvadoran army launched major offensives along the main road connecting the two nations and against the Honduran islands in the Golfo de Fonseca. At first, the Salvadorans made fairly rapid progress. By the evening of July 15, the Salvadoran army, which was considerably larger and better equipped than its Honduran opponent, pushed the Honduran army back over eight kilometers and captured the departmental capital of Nueva Ocotepeque. Thereafter, the attack bogged down, and the Salvadorans began to experience fuel and ammunition shortages. A major reason for the fuel shortage was the action of the Honduran air force, which--in addition to largely destroying the smaller Salvadoran air force--had severely damaged El Salvador's oil storage facilities.
The day after the fighting had begun, the OAS met in an urgent session and called for an immediate cease-fire and a withdrawal of El Salvador's forces from Honduras. El Salvador resisted the pressures from the OAS for several days, demanding that Honduras first agree to pay reparations for the attacks on Salvadoran citizens and guarantee the safety of those Salvadorans remaining in Honduras. A cease-fire was arranged on the night of July 18; it took full effect only on July 20. El Salvador continued until July 29 to resist pressures to withdraw its troops. Then a combination of pressures led El Salvador to agree to a withdrawal in the first days of August. Those persuasive pressures included the possibility of OAS economic sanctions against El Salvador and the dispatch of OAS observers to Honduras to oversee the security of Salvadorans remaining in that country. The actual war had lasted just over four days, but it would take more than a decade to arrive at a final peace settlement.
The war produced only losses for both sides. Between 60,000 and 130,000 Salvadorans had been forcibly expelled or had fled from Honduras, producing serious economic disruption in some areas. Trade between the two nations had been totally disrupted and the border closed, damaging the economies of both nations and threatening the future of the Central American Common Market (CACM). Up to 2,000 people, the majority Honduran civilians, had been killed, and thousands of other Hondurans in the border area had been made homeless. Airline service between the two nations was also disrupted for over a decade.
Sorry Kocjo, but it's hard to be precise about the reasons for a war.
Best Regards, David