Why did pachacuti decide to attack the ayarmacas

"Pachachuti" decided to attack the Ayarmacas because the Ayarmacas didn't pay homage to the Incas, especially their ruler, Tocay Capac. Pacachuti wanted to conquer all of the kingdom's nations and those who didn't surrender to his will were killed or destroyed.

Explanation:

Pachachuti was an Inca ruler who became very active in bringing the entire kingdom's regions under his control. The Incas then followed his conquest by extending the boundaries. This required all young men to become part of the army. This made the Incas even stronger. They also regulated the new areas which were colonized by placing a noble person who was of high-rank for every region. Forced labor was imposed in order to accomplish the projects of the kingdom.

The Ayarmacas were a nation of Indians who were against the Incas. They went against them and thus, it angered Pachachuti. This led to their fighting in Guanancancha which resulted to the destruction of the Ayarmacas.