السلام عليكم ورحمة الله وبركاته
There was unity when Muslims had strong faith in Allah and Islam and followd the Holy Book of Allah SWT and the Sunna of his Prophet SAW, Then Muslims started loosing that unity little by little when hypocrites started to make Fitnah in the Muslims communities which lead to the lack of faith..
(Surat Al-Imran 3)And hold fast, all of you together, to the Rope of Allâh (i.e. this Qur'ân), and be not divided among yourselves[], and remember Allâh's Favour on you, for you were enemies one to another but He joined your hearts together, so that, by His Grace, you became brethren (in Islâmic Faith), and you were on the brink of a pit of Fire, and He saved you from it. Thus Allâh makes His Ayât (proofs, evidences, verses, lessons, signs, revelations, etc.,) clear to you, that you may be guided. (103)
Thats why most Islamic countries don't Apply most of the Islamic rulings, Which lead to the fast growth of crime rates. And if our Islamic countries (Muslim leaders) continue to do that, Then there will come the time when Islamic communities become just like the non-Islamic.
Prophet Muhammad Salla Allahu Alahi Wasalam said: “There will come a time of patience when the one who adheres steadfastly to his religion will be like one who holds a burning coal.”
(Narrated by al-Tirmidhi, 2260; classed as saheeh by al-Albaani in al-Silsilah al-Saheehah, 957. )