Italian troops under General Emilio De Bono crossed the Mareb from Eritrea into northern Ethiopia without a declaration of war, and took Adwa within days; it was 1935, and the fighting went on until May of the following year. Thousands of Ethiopians were killed in the months that followed, many of them in villages far from any front line.
In Geneva the machinery moved quickly at first. The Council found Italy in breach of the Covenant within the week, the Assembly agreed sanctions, and the list of goods was drawn up with care: arms, credit, rubber, metals. Oil was discussed and set aside. The Suez Canal stayed open to Italian shipping the whole time.
The Mareb is the border river, and past it the ground climbs fast into highland at around two thousand metres. There were almost no roads to carry supply, so after Adwa the advance slowed to the pace of the road-building parties and the mule columns feeding them, which is part of why those first weeks looked the way they did.
Adwa was not a random first objective: it was where Ethiopia had broken an Italian army in 1896, and that memory was very much alive in 1935. The Ethiopian Orthodox Church was woven into the resistance that followed — Abuna Petros, who refused to tell people to submit, was executed in Addis Ababa the next summer.