Different sects in Islam

Why is there even? Allah subhanahu wa ta ' ala has commanded us United and prohibits us from being divided in different groups and cults. There is only one religion, only one way accepted by Allah, and it is al Islaam. The religion of Islam needs no religious innovations, it has been perfected by Allah, so we will not corrupt the it, but we will take the path that the Prophet Muhammad, aleihi wa sallam - salallahu and his companions were 1400 years. Allah says in the Holy Koran:

إِنَّ الَّذِينَ فَرَّقُوا دِينَهُمْ وَكَانُوا شِيَعًا لَّسْتَ مِنْهُمْ فِي شَيْءٍ ۚ إِنَّمَا أَمْرُهُمْ إِلَى اللَّـهِ ثُمَّ يُنَبِّئُهُم بِمَا كَانُوا يَفْعَلُونَ "" surely they that divided into parts of their religion and became sects, you have no problem with them; their case is only with Allah, can he find out what they have done. ""