When several thousand Ethiopian soldiers recently entered Somalia, at the behest of one faction in a looming civil war, the reaction among most Somalis was quite hostile. Most people would expect that, since the two countries are neighbors, and have a history going back thousands of years. But there's more to it than that. Until about half a century ago, Somalia didn't even exist as a country, while Ethiopia is one of the oldest empires in Africa, second only to Egypt. Not only that, but Ethiopia has been a Christian state for nearly two thousand years, and is the only part of Africa that was never subjected to colonial rule.
Until 1959, when Italy and Britain combined their Somali colonies into a single Somali state, Somalia was never a country. There were trading towns along the coast, dominated by Arab and Indian merchants. Most Somalis lived inland, living as farmers and herders. Their only government was clan and tribe elders. The clans fought each other, and the coastal towns. When British and Italian troops showed up in the late 19th century, to establish colonies, the coastal towns went along, the clans in the interior generally did not.
The Somali language was unwritten, and a written form was not invented until the 1970s. The educated classes had learned their lessons in Arabic, Italian or English. The new nation was united by language and religion (Islam) but divided by social class and clan affiliation. There was also a problem with part of eastern Somalia (or eastern Ethiopia), called the Ogaden. Britain settled this dispute by giving the Ogaden to Ethiopia when they left in 1959. Actually, over the last few centuries, Ethiopia had controlled much of modern day Somalia. But whenever the Christian Ethiopians came out of their highland strongholds and tried to approach the Somali coast, they were attacked by the more numerous Moslems in the region. Arabs, Turks and Egyptians were all opposed to Ethiopian control of the Somali coast. The Ogaden was another matter, and it became something of a neutral zone. But it was used mainly by Somali herders, and the new nation of Somalia considered the Ogaden to be part of Somalia.
The new nation fought, and lost, a war with Ethiopia in 1964 over the Ogaden. Another war was fought in 1977, and that one pretty much destroyed the Somali army. That, in turn, helped bring about a government collapse in 1990, and anarchy ever since. Many Somalis still want the Ogaden, and hate the Ethiopians for not giving it up.
In another irony, the Ethiopians want to help the fragile "transitional government" in Somalia because the main opposition to this government is led by Islamic conservatives. Ethiopia has a long memory when it comes to Islamic conservatives, and how Moslem troops have ravaged Ethiopia in the past, often coming very close to conquering the country. The Ethiopians don't want Islamic conservatives running Somalia, and would consider it a victory if they could just prevent that.
Ethiopia and Somalia are about to go to war again, because of a dispute over a lot of semi-arid and thinly populated land (the Ogaden), and generations of ethnic and religious hatreds. Ethiopia usually wins these wars, and there have been many of them in the past.