Why did Justo Rufino Barrios invade El Salvador in 1885?

Justo Rufino Barrios, who served as the president of Guatemala from 1873 to 1885, invaded El Salvador in 1885 as part of a persistent effort to restore the five-nation federation that had collapsed in 1838.12

Barrios was a staunch advocate for Central American unity and believed that if diplomatic efforts failed, the union should be imposed by force. After his attempts to revive the old federation through political persuasion proved unsuccessful, he declared himself its ruler in 1885 and marched his army into El Salvador to enforce unification. This military campaign ended in his death at the Battle of Chalchuapa on April 2, 1885.12