The main achievement of Arzú's presidency was the signature of a peace accord with the guerrilla group Guatemalan National Revolutionary Unity, which ended Guatemala's 36-year-long civil war. The negotiations had been going on since 1990, and Arzú gave them a vital new impulse when he met the URNG in Mexico on February 26, 1996. A ceasefire followed on March 20, and various peace agreements were signed as the year progressed. On December 12, an accord legalizing the URNG was signed in Madrid. On December 18, Congress passed a law giving a partial amnesty to the combatants, before the final accord for a firm and lasting peace was signed on December 29.