When is loyalty to disbelievers an act of disbelief (kufr), and when is it merely forbidden (haram)?

The manifestations of showing allegiance to disbelievers vary, some of which constitute disbelief (kufr), some are major sins (kaba'ir), and some are less than that. Muhammad ibn Saeed al-Qahtani, in his book "Al-Wala' wal-Bara' fil-Islam" (Loyalty and Disavowal in Islam), mentioned forms of allegiance that differ in their ruling. Some of them necessitate apostasy, such as loving disbelievers for their disbelief, while others are major sins, such as exalting them and praising them. Among the forms that lead one out of the fold of Islam are: being pleased with the disbelief of disbelievers, showing them general allegiance, believing in some of their doctrines, compromising the religion for them, and sitting with them when they mock the verses of Allah.