Want to understand if the tensions between Shia/Sunni/Alawites etc. have always been a component of Syrian history or whether these are more recent developments.
Syria has been 'colonially' ruled for most of its history, from very ancient times until after WWII. So, as most of Syria's history is colonial, much of the origins of anything in modern Syria can be considered to have been influenced by 'colonial rule'.
Starting in about the 18th or 19th centuries BC, Eastern Syria was occupied by the Old Assyrian Empire and the Babylonian Empire. In about 1600 BC Western Syria was conquered by the Hittites (from Asia Minor). There were then many centuries when Syria was fought over and occupied by the Hittite Empire, the Mitanni Empire, the Egyptian Empire, the Middle Assyrian Empire and the Babylonians.
In the 11th century BC, with the decline of the Hittite and Assyrian Empires, there was a period where Syria was ruled by a collection of local states.
In 911 BC Syria was conquered by the Neo Assyrian Empire. In 605 BC it was taken over by the Neo Babylonian Empire. In 539 BC it was conquered by the Persian Empire. The Greeks under Alexander the Great took Syria in 330 BC. It then became part of the Greek Seleucid Empire.
Syria was briefly taken by the Armenians in 83 BC, but then conquered by the Romans in 64 BC.
In 640 AD, Syria was conquered by the Muslim Arabs. The Umayyad Dynasty of Caliphs made their capital in Damascus in Syria, but in 750 AD the Umayyads were overthrown by the Abbasids, and the capital moved to Baghdad.
Sections of Syria were ruled by the Crusaders between 1098 and 1199, and the rest was ruled by Seljuk Turks. Saladin (a Kurd) conquered most of Syria between 1175 and 1185. The Mongols invaded in 1280.
The Mongols were defeated in Syria by the Mamluks (from Egypt), who then ruled Syria. In 1400, Tamurlane conquered Syria and massacred the inhabitants of Damascus, and many in the countryside.
In 1516, the Ottomans conquered Syria from the Mamluks. Syria remained part of the Ottoman Empire until WWI. After WWI, (in 1920) Syria became a country with roughly its current borders under a French Mandate.
After WWII Syria became independent, though from 1958 until 1961, it joined with Egypt in the United Arab Republic.
Since Syria has been a colony for almost all of its history, it is virtually certain that most factors in modern Syria were descended from events during ‘colonial rule’ sometime in the past.