It was Cyrus II the Great who united the divided tribes of Persia around 559 BC. At the time, the Persians were subservient to the Median Empire ruled by Cyrus' grandfather, Astyages. Cyrus rallied the Persians together and revolted, throwing Astyages from power. Cyrus, now Shah of a united Persian kingdom, conquered the rest of Media and their large Middle Eastern empire in 550 BC.

Here's my question:

Of unsure strength from King to King,
We first found hope in Lab.
From the north we came, met with Med
And even brushed with Bab.

Who are we exactly?