This era was started by Constantine VI, nothing really significant happened in his reign, but he was the first emporer in almost 200 years to not constantlly go on campaign. The first 60 years of this era were more of consilidation of power then expansion, the Byzantines had learned from their mistakes and wouldn't expand unless they knew they could hold onto it.
New age of expansion
Around 840 they regained the western Balkens, (which was made up of several small kingdoms) to restore the Danube frontier, the Danube now controled either by them or the Bulgarians. For almost next one hundred years the Byzantines were waiting as bit by bit the Bulgarians were getting weaker, in the early 10th century the Byzantines invaded and was a disaster, it be almost another one hundred before they invade again. Nikephorus, evan though he reigned only for 6 years he manged to bring Cyprus, Crete and Antioch back under their control, these may seem like minor conquests but the Arabs had fortified these into major fortesses to try pretend the Byzantines to return as a major Meditarian power.
The part of Basil's reign saw territorial loss, civil war and invasion, but due his constant campaigning, he managed to hold the Empire together, he restored the Danube frontier, unlike the Emporer over hundred years ago, his invasion of Bulgaria was more gradual.