It was mostly an issue of regionalism. When the ruling class of each region of the Republic of Colombia (Gran Colombia) realised that they could govern themselves independently, many in Venezuela and Ecuador began to think that having the capital in Bogotá just meant changing the "colonial overlord" from Madrid to Bogotá, so they began to form groups to achieve independence from Gran Colombia. Moreover, Bogotá could not effectively control all the territory, in part because Bolívar left the government a bit unattended to keep fighting the Spanish in Perú and Bolivia, and the regional governments began to have even more power under the federalism of the nation. Santander, the vice-president that ruled while Bolívar was away fighting, seemed to prefer the idea of more autonomous regions as well, which then led to independent republics, while Bolívar wanted a more centralized government centred on him. Bolívar's ideas would go on to form the modern day Conservative Party of Colombia and Santander's ideas would create the modern day Liberal Party of Colombia.
What I meant by what I said is that before the Colombian Constitution of 1991, the older Constitution said that all Colombians, in order to be considered part of the "Colombian Nation" must share a common Spanish culture, language and Catholic religion, basically just including white and mestizo Colombians of Spanish heritage. This meant that the indigenous people, protestant immigrants and Afro-Colombians where not allowed to vote or hold public positions. Foreign Catholics could acquire citizenship if they learned Spanish. An Apartheid-like system never existed in Colombia, aside from denying the possibility to vote to the groups I mentioned, the nation established laws and rights that applied to all of its citizens and, even though racism existed, it never became as strong or legally sanctioned as in South Africa or the USA, though natives and afro-Colombians still had worse living conditions. But in 1936 the old Constitution was modified and all male citizens were allowed to vote, regardless of ethnic and cultural background, even though the Constitution still stated that Colombia was a Spanish Catholic country. In 1954 women were allowed to vote. What I meant by the 1991 date is that it was only until the 1991 New Constitution that all ethnic groups in Colombia where legally recognized as part of the "Colombian Nation" and their languages, territories and particular rights were legally recognised.
Not really, since the late 19th century, despite what the Constitution said, most people in Colombia began to regard themselves more as Colombians than as mestizo, Spaniard, afro-Colombian, etc., most native groups did kept their languages and identities and Universal Suffrage was, at least in theory, guaranteed for everyone since 1936 for all men of all ethnicities and included women in 1954, way before the Civil War began. The main issue that caused the Civil War was the power struggle between the Conservative Party (based in Bolívar's ideas) and the Liberal Party (based on Santander's ideas). Since Bolívar's death all the presidents of Colombia were from these two parties and the appearance of any other party with a different ideology was not permitted. This, together with the vast amounts of lands controlled by a few owners of the haciendas and large scale farms in the country, prompted the appearance of communist peasant groups backed by the Soviet Union that wanted to overthrow the US backed government of Colombia. The Civil War in Colombia was basically a proxy war of the Cold War.
Universal Suffrage for all ethnicities existed since 1936 and for woman since 1954, not since the Constitution of 1991. The communist groups, which had lost a great part of their ideology by the second half of the war, took advantage of the disorder of the war to began trading with drugs, as did Pablo Escobar, and both did atrocious acts for the duration of the war which is why they were declared as terrorist organisations by most western countries. It has never been confirmed if Pablo Escobar participated in the attack to the Supreme Court, but some people think it was likely he did, together with other terrorist groups. However, the Constitution of 1991 was indeed a response from the country to create a more egalitarian legal framework for the nation. It recognised the existence of various other political parties and gave more rights and autonomy to natives, afro-Colombians and guaranteed more laboral rights for peasants and workers, all of this in an effort to avoid a similar conflict in the future. This, together with the Peace agreement signed in 2016, formally ended the war, though various insurgent groups still exist, the country is much more safer nowadays than it used to be back in the 1970s and 1980s, the worst part of the conflict.
I think I won't be replying more to my original post because I've said it all and the purpose of this thread is to discuss the new additions to the game, so I won't extend myself anymore on explaining Colombian history. (Again, sorry for any bias or imprecise information I could have said)