Background, I'm Oromo and hence study Oromo history extensively as well as of course know literal family history.

The answer to your question can be summarized in the following 19th century story of an exchange between King Menelik's Ethiopian Military vs Oromo's Republic Military as outlined in "Abbas Gnamo's" Conquest and Resistance in the Ethiopian Empire. These aren't the exact words but I'm gonna summarize

The Oromo Commander says to the Ethiopian commander:

"your guns make you swell with pride. Throw them on the ground and measure yourself up with me. You will see that I am strongest. If you drop your guns, one of my regular warriors will be worth five of yours and one of my bravest soldiers will crush an entire one of your battalions"

To which the Ethiopian/Abyssinian commander responded:

"If I laid my gun to the ground, I know you'd be my winner as you always have been before. No I will not drop my gun. Go and grind flour and present to me your tribute. Get on your knees and declare me as your liege"

King Menelik (Ethiopia) always gave the people he conquered the opportunity to submit before he attacked. Hence the "go grind flour and present tribute (taxes)".

Of course I could've just answered this question simply by saying "guns". But what fun is that. This is a history sub anyway.

Fun fact, the Oromos of the Jimma Kingdom in fact were actually accustomed to matchlocks, but they just didn't like them and would yet still regularly crush any Ethiopian invasion attempts. This was before Menelik got his hands on more advanced firearm technology at the time though