Not here for the taking
In 1160 Owain Gwynedd invaded Powys. His aim was to exploit the leaderless state of the kingdom, after the recent death of King Madog and murder of his heir, Llywelyn. We don't know for certain if Owain was behind their sudden removal, but he certainly profited from it.
The invasion was halted by Roger Powis, a Welsh castellan in royal service, who garrisoned the castle of Edeirnion against him. Owain paused to build a castle at Tafolwern, to secure control of the territory he had already annexed.
However, Tafolwern lay adjacent to the kingdom of Arwystli. This was ruled by King Hywel ab Ieuaf, who objected to the sight of the Venedotian army camped on his border. In 1162 Hywel launched a raid that destroyed Owain's new castle, which provoked a counter-raid into his own lands. This conflict distracted and weakened the forces of Gwynedd as they were poised to drive into Powys.
After the death of their king and his heir, the ruling class of Powys fragmented. The Brutiau record that a son and nephew of the late King Madog, Owain and Maredudd, had joined Owain Gwynedd. The rest of the Powysian elite chose to resist the invasion. They were given considerable financial and military aid by Henry II: the Pipe Roll for these years shows at least seventeen individual payments to Powysian lords, subsidised to fight Owain.
This was a divide-and-rule policy on the king's part; it was in his interest to play off the Welsh kingdoms against each other. On the other hand, the Powysians wished to retain their own independence, and so far Owain Gwynedd had offered them nothing but violence. At least, by taking Henry's money, they kept him at arm's length too. Powys was an ancient kingdom, with its own laws and customs and traditions. It wasn't just there for the taking.
So, Owain's unity project wasn't going very well. His invasion of Powys had only succeeded in driving the Powysian lords (or most of them) into the arms of the king of England. He had also managed to provoke the King of Arwystli, who refused to bow the knee to the self-styled 'Princeps Walliarum' - 'Prince of the Waleses'.
Which was all deeply unpromising. Then, in 1165, everything changed.