Cliff notes(hard to do without leaving out important points for context):
Back in the 70s and 80s, Eritrean independence fighters (EPLF-Eritrean People’s Liberation Front/Isaias Afewerki-current president since independence in the 90s) combined with Tigrayan based independence fighters (TPLF-Tigrayan People’s Liberation Front/former PM Meles Zenawi whom passed away from an illness), Amhara militias against Mengistu, and Oromo independence militias (OLF-Shane) combined to eventually overthrow the communist dictatorship in the early 90s. After being overthrown, Col. Mengistu Haile Mariam escaped to Zimbabwe where he lives today, the former dictator predicts that the TPLF will one day tear the country apart starting with Eritrea.
The EPLF go on to establish Eritrea and Ethiopia becomes landlocked, TPLF takes control of the Ethiopian state. Beforehand, they promised the OLF (Oromo militias) a similar setup to Eritrea with their own land called Oromia but later double crossed and stomped out theirs and any separatist movements including prison, torture, media censorship, extra judicial killings, etc.
TPLF/Meles create a ethno-nationalist based system on the grounds of ethnic/linguistic demographics. This was argued as being a system which gave ethnic groups more authority and freedom including respect of other groups and cultures. In truth, it was a clever system of divide and rule which made managing the different groups easy. Two generation of Ethiopians were taught tribe over nation and created more radicalized youths willing to kill their neighbor because of ethnicity
Meles and Isaias began to feud over territorial rights and dragged Ethiopia and Eritrea into a bloody border war. After the ceasefire, the TPLF maintained hostilities and a 20 year cold war split apart families and communities. Mass deportations of longtime Eritreans citizens in Ethiopia and Ethiopian citizens in Eritrea solidified the state of no war no peace
TPLF went on to loot much of the resources and land including a great deal of foreign currency. This was all while Ethiopia saw among the most rapid economic growth in the world. But vulnerable tribes had their land sold to foreign nations by Tigrayan elites while the people had no redress. The Hunter gatherer societies of the Omo valley being among their many victims. The death of Meles Zenawi (the architect of the dam project as well as an efficient police state apparatus) weakened the power of the TPLF as their leader was now gone and difficult to replace which began their downward spiral. The TPLF then installed the puppet PM Desalgn from one of the smaller tribes in the south to appease groups grumbling about the overly Tigrayan character of leadership while attempting to maintain the police state. Amhara and Oromo youths unite in mass protests which hadn’t been seen for years in the country. The TPLF’s hand is forced by the civil rest which bring in Abiy as a transitional leader, but by now the Tigray area has become a highly militarized region due to the history of the wars with Eritrea hosting a sizable portion of Ethiopia’s heavy artillery and missiles as well as a militia and paramilitary force rumored to be around 250,000 as well as having controlled the economy and military for years which kept them both very wealthy and very powerful and very prepared for potential war.
Abiy’s reforms essentially triggered things. He’s a product of the TPLF apparatus itself as a former soldier and intelligence officer. There are investigations being conducted into stolen funds and shady corruption of the TPLF regime and this gave Tigray elites a feeling of persecution which TPLF sold to its people as an attack on them all. The peace in Eritrea was the second major trigger. The TPLF wasn’t involved in the peace talks despite the border conflict directly involving them. This could be seen as one of Abiy’s main errors however there’s no evidence to suggest that the TPLF were good faith actors in the talks nor is there evidence that they attempted to participate at all. Nevertheless, the peace with Eritrea meant land concessions that were beyond what the TPLF could accept.
The final straws came when Abiy dissolved the old EPRDF (Ethiopian People’s Revolutionary Democratic Front) which is the name of the ethnonationalist based system which the TPLF and Meles created in exchange for the “Prosperity Party” which is an attempt to introduce a non ethnic based political system which allows membership for all regardless of ethnicity and presents a Unitarian approach vs an ethnic based one. All groups except for the TPLF joined the new coalition which further alienated them. By this point, their power and influence on a national level was crushed considerably so they retreated to their regional capital of Mekele and began provocative actions to defy Abiy’s authority.
Elections were supposed to be held this year but were held off due to Covid. TPLF saw this as an attempt by Abiy to extend his mandate. Bear in mind, Abiy is a transitional leader and still has to face the electoral process. In defiance of Abiy’s call to postpone elections, the TPLF carried out elections in Tigray and naturally won in a 100% landslide. Abiy called their elections illegitimate and declared the TPLF illegal, the TPLF did the same saying Abiy’s mandate officially ended on September 15th and there’s currently a constitutional crisis. Federal govt cut off the whole Tigray region from the budget and dissolve their govt and pull their terrorist card.
The final straw came when TPLF forces conducted a sneak attack on the Ethiopian army’s northern command in Tigray region in an attempt to steal weapons and force soldiers to defect. Abiy declares a state of emergency and vows to eliminate the criminal element. But with a generation that’s been taught false narratives and fascist ideals, the TPLF have many fault lines they can exploit to foment further chaos in the country. Their strategy is scorched earth and the longer Abiy let’s this linger the worse this conflict becomes.
Nominally, this is a regional proxy war between Ethiopia and Egypt via the TPLF over the Nile as the TPLF had foreign benefactors during their struggles and were always the obvious ally in Egypt’s quest to maintain Nile hegemony. But majority of this has to do with 30 years of criminality finally being answered for and rather than quietly retiring with the millions they stole from Ethiopian banks and industries they’d rather wage war and bring all of their people down with them.