But after Abiy Ahmed became prime minister, they refused to join his single party alliance.
They've also resisted his sweeping reforms.
And in September, they went ahead with local elections, defying Abiy's decision to suspend polls.
He now says his patience has run out with Tigray.
He's ordered a military operation in the region after accusing the TPLF of attacking federal troops.
It's feared the feud could lead to the break up of Ethiopia.
Just what are the causes of tension there?
Presenter: Mohammed Jamjoom
Awol Allo, Lecturer at Keele University and a Horn of Africa analyst.
Zadig Abraha, Ethiopian minister in charge of democratization
Martin Plaut, senior research fellow at the Institute of Commonwealth Studies.
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