The Byzantine Empire
John II Comnenus (1118-1143)
The Empire had the good fortune of having one good emperor succeed another. John II was a wise ruler, effective field commander, and enjoyed a long reign.
Like his father, John spent much of his career in the field, fighting one enemy or another. At the beginning of his reign the conflict was with Venice, which had won great privileges under Alexius that John tried to remove, with little success.
Then came wars with the Petchnegs, the Serbs, and even the Hungarians, all of which turned out much better than had the war with Venice. In the 1130s, he campaigned in Anatolia with great success. Some of these successes required repeating, as the Turks would win back what they had lost as soon as the Byzantine army retired, but John persevered. He also won major victories against the Armenians in Cilicia.
This was the emperor who brought an army right down into Syria and forced Raymond of Antioch to recognize him as overlord. Only outright trickery kept the city out of Byzantine hands.
John died at a fairly young age while hunting. He had extended his father's gains, placed the government on even firmer ground, and looked like he might extend Byzantine influence into Syria once again. After terrible trials in the 11th century, the Byzantine Empire was once again healthy and strong.