[After the National Resistance Army (NRA) victory, Uganda] remained in turmoil, especially in the north, where rebels loyal to Obote and Okello fought the government. In 1988, Museveni called on all insurgent organizations, including the Uganda Freedom Movement, the Federal Democratic Movement (FEDEMO), the Uganda People's Democratic Army, and the Uganda Federal Army, to lay down their arms, without success. Nonetheless, Museveni strengthened his grip on the government and managed to check rebel resistance with help from the NRA, which mounted successful offensives in the Soroti and Kumi districts in 1990. Clashes between Rwandan troops and Ugandan guerrilla forces on the border strained relations between the neighboring countries, resulting in their signing a security agreement in 1992. Tensions in Uganda eased when the constitution was amended (1993) to allow for the reestablishment of tribal rulers in four old southern kingdoms. But Museveni, backed by the Constituent Assembly, successfully opposed the reintroduction of multiparty democracy, while carrying on a program of economic reform with generous aid from other countries. In 1995, rebel offensives were suspended in the central and southeast regions... In 1997, Museveni received US arms and military training for his actions with Sudan and the Congo (Zaire).