As mentioned you will get totally different perspectives depending on who you ask.
This is my personal understanding and should be taken with a grain of salt.
Abiy Ahmed( a former intelligence officer) was picked to handle a transitional government after years of regional and ethnic (for lack of a better word) tensions.
The ruling party at the time was Tigray dominated and was facing increasing pressure to share power. Abiy Ahmed is half Amhara and half Oromo so this probably factored into his being chosen.
As soon as he took the reigns of power so to speak he started facing serious pushback.
Tigray who felt they were being blamed for a multitude of problems, Oromo who have felt historically marginalized and were seeking greater representation and territorial claims as well as Amhara who as the majority also felt marginalized and also had historical territorial disputes.
The Tigray ( who for most of Ethiopia’s recent history have been over represented in government and army) felt that his call to delay elections (he was supposed to be a gap stop until elections) was a power grab.Who attacked first is disputed but Tigray elements and the army clashed.
Abiy clamped down very hard.
This is where it gets very touchy. Amhara militias were used to suppress the rebellion and turned out into a serious conflict ( this is where the territorial claims come in, there were many disputed areas that the Amhara believed were historically theirs and they wanted them back).
Sudan borders the region of Tigray and Ethiopia made a deal with the Sudanese government that they would remain neutral and not arm the Tigray.
To add fuel to the fire there are credible claims that Eritrean soldiers were conscripted to quell the ‘insurrection’ and committed atrocities ( Eritrea has a historic grudge with Tigray as the war between the two countries was mostly Tigray led as well as thousands of Eritrean refugees heading to Tigray as a safe haven, which the Eritrean government sees as a huge embarrassment).
AND
Sudan has a historical border dispute with Ethiopia with very fertile land being farmed by Ethiopian farmers by mutual consent until a solution was found.
Making good on the chaos the Sudanese army started taking back this land. The skirmishes are increasing in length and intensity and could very well turn into a war.
This is very condensed and there so many nuances and geopolitical issues that play into the conflict.
If I made any factual errors I’d welcome the correction.

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