The party was pretty illegal until the end of the French mandate, its activities restricted to participation in violent anti-colonial demonstrations. It always considered itself a pan-arab party, so it founded itself in a national (pan-arab) and a regional (individual arab countries) structure even before taking off. It always had some appeal for christians and non-muslim groups outside of Palestine and Lebanon, who saw secular nationalism as a way to become equal co-citizens with the muslim population around them. It was also very attractive to merchants, students and intellectuals who were fed up with the incompetent and corrupt old guard of Arab Nationalism, mostly landowners, a bunch of propped-up clerics (see al-husseini in Jerusalem) and so on who all had cooperated with the west and zionism and bickered among themselves, finally getting smashed to bloody pieces in the war leading up to the Nakba, 1947 and 1948.

Independence 1946 allowed for some activities. The party was not just running on anti-colonialism, but on a moral message about regeneration and rebirth. The very christian elements of ba3th came from Michel Aflaq, a christian. Individual party members would go around villages and assist however they could, often as doctors. This led to some mild success. The party's extremely elitist and idealist approaches kept it from taking off for a considerable amount of time.

Immediately after the disastrous failures against Israel, Syria went through 3 presidents in a single year, all militarily couped, leading to military guy Adib Shishakli taking power. He banned all parties. Big Mistake. In illegality and exile, the ba3th fused with the Arab Socialist Party, that had been pretty successful in Syria organizing peasants. It also led to the more differentiation between the national and regional levels. This led to it slowly taking more socialist positions and the, albeit not very ideologically firm (for some exceptions) socialist wing of the ba3th to become stronger at the expense of the more disgusting nationalists. After Shishkali suspended the constitution, the rest of the military had enough and deposed him with the support of a coalition of basically every party.

This led to tense back and forth, I am already taking too long. in 1958 the ba3th was in charge, but in a politically very insecure position and fused with Gamal Abdel Nasser's Egypt to hold onto power, somewhat against its own will. Today, the arab elite will blame the period of the United Arab republic failing on "cultural differences". It was, quite frankly, Nasser's massive and monumental ego that didn't allow for any party outside of his Arab Socialist Union Party and his desire to see Egypt on the top of any unified Arab state. Not that the Ba3th was not also full of people with massive egos, who were seething with rage at the fact that Nasser dissolved all but his party, some branches ignored this and stayed active, recruiting members rom their own religious sect. In any case, syria was getting the short end of the deal, so the military couped and deposed the ba3th 1961. The refounding and reorganization of the ba3th in the wake of this led to hasty promotions along "sectarian" (read: confessional) lines, which were still the predominant form of loyality and social connection during that time for a host of reasons. These promotions absolutely destroyed party discipline.

The two trends of the military routinely intervening in syrian politics in mostly unbloody coups (unbloody til ~1965) and promotions and loyality running along the lines of a religious community (which worked very different from attending mass/friday prayer once a week, imagine if your leftist sect was inheritable and you couldn't convert away easily) dominated the 60ies. The ba3th couped itself into power again, this time led by the more socialist oriented party members and officers, who had their disticnt subgroup in the party and heavily recruited along religious lines as well. A Sunni leader would have Sunni soldiers across the ranks behind him who would listen to him instead of their actual superior, a druze had druze guys etc. This ragtag group decided that the party was gonna be hardcore socialist (at least what they thought to be socialism), goddammit, so they mobilized all their support to get a huge bunch of motions through during the party's congress which. The final charter for the 1963 used super communist language and had a bunch of points about how things were to be done. This was promptly ignored in general, party discipline having become pretty much a joke. Michel Aflaq, a nazi-curious petty bourgeois dreamer, was NOT happy and still in charge of the national (pan-arab) level of the party (iirc). The increasing split and infighting within the party became charged with sectarian (in a religious sense) feelings bc of the power dynamics () alongt the sectarian lines of loyalty. Aflaq and his dudes got kicked and went to Iraq where Saddam ate them for breakfast (I don't know the details there, but Saddam was a more ruthless, more powerful, more cunning politican than Aflaq for sure and he faded to irrelevance in syria).

Open Sectarianism was outlawed by the secular ba3th, but the suspicion of secretly being sectarian was often projected onto others. This led to more and more coups and purges by the military, often along sectarian lines, so after some time, sunnis, christians, and finally the druze went out, until only the Alawite leadership was left by 1967. Repeatedly purging your military is not good for its abilities, ask .

So when the war with Israel 1967 became inevitable, the military officer Salah Jadid was in charge of Syria. He had a decent socialist program and was puppetered by the communist group of the "three doctors", but was pretty fucking clueless himself (he called using the Palestinian bataillions loyal to syria a "people's war" in reference to Mao). The Arab armies lost in a hilariously bad manner. I can't overstate that, there is no way around that. I don't have details on the war itself. I only know It was a depressing fucking curbstomp for Syria. Egypt had some chances, had its airforce survived. But the Syrian front was a total wash. Salah Jadid was a dead man walking from that point on. Hafiz al-Asad, a fellow Alawite, prepared his coup and took power 1970. He quickly cemented some rule, cut some deals with the sunni petty bourgeoisie, who didn't thank him at all for that. I am exhausted now and need to start my day. I skimmed over a lot of details and probably misremembered a bunch of stuff, Patrick Seale and Hanna Batatu are excellent authors for more background information.