Why are there tensions in the Horn of Africa?

Egypt has offered to send 10,000 soldiers to Somalia to assist the country with peacekeeping operations. However, this seems to have unsettled Ethiopia which has said it could not “stand idle while other actors take measures to destabilise the region.” Ethiopia has been a key ally of Somalia in its fight against the militant group, Al-Shabaab. So what exactly has caused these tensions? And what has the Ethiopian Grand Renascence dam got to do with all this? Alan Kasujja has been exploring for Africa Daily.