The army of El Salvador went into action for the first time ever on this day in 1969, crossing the border to invade neighbouring Honduras and beginning the conflict now known as ‘The Football War’.

Tensions between the neighbouring countries had been rising for a number of years through disputes over their ill-defined shared border, and the influx of thousands of mainly poor immigrants from overcrowded El Salvador into the sparsely-populated south west of Honduras.

Resentment began to grow among Hondurans, especially in rural areas. Under political pressure, the Honduran government had enacted land reforms that by 1967 were resulting in the expulsion of thousands of Salvadorians, who returned with tales of ill-treatment at their neighbours’ hands.

The two nations were also facing off in a qualifying group to reach the 1970 World Cup finals. Honduras won the first match in their capital Tegucigalpa on June 8, 1969, after which violent clashes occurred. A week later, the return game in San Salvador saw the home side claim a 3-0 victory.

Rioting in the wake of the second game saw lives lost among fans of both nations, but a play-off match, played in neutral Mexico City, was now required to separate the teams. El Salvador scored in extra time to win 3-2 and advance to a final match against Haiti to determine qualification.

The El Salvador team ahead of the World Cup play-off against Honduras in Mexico City.

On the same day, El Salvador’s government cut diplomatic ties with Honduras, for failing to punish alleged crimes against Salvadorian immigrants, or offer any reparations for their expulsion.  The following day, Honduras followed suit.

[Read more: April 3, 1982 - Parliament dispatches task force to fight for the Falkland Islands]

As tensions rose, a number of border skirmishes occurred until El Salvador launched their assault by land and air on their neighbours on July 14.  They would advance 8km, taking nine cities, until their advance was halted by a lack of ammunition and fuel.

The Organization of American States (OAS) intervened and forced a cease-fire on July 18, though El Salvador did not withdraw its troops until August 2. Estimates of the number killed in the conflict range as high as 5,000, with tens of thousands more displaced by the fighting.