The Galactic Union's First Contact with humanity was initiated by the Buma, who are known for seeking out new races.
A hyperspace-shunt enabled scout ship visited Earth in the early 1900s and reported back to the Union that humanity was at a pre-Industrial stage of development.
In the early 21st-century, a Buma scout ship looking for untapped sources of revenue passed close enough to Earth to pick up our radio waves. Despite the possibility that Earth could not provide sufficiently valuable trade goods at their current technology level, the Buma asked the Cartography Guild to install a stargatestargate in the Sol System and initiated contact.
At first, the gamble looked to be a failure. Buma leaders doubted they would recoup their investment since all Earth offered in trade were a few rare earth and radioactive elements and the ability to extract them.
This changed during the initial negotiations to make Earth a provisional member of the Union, when terrorists killed the Buma representative and two of his MinSha mercenary guards. The MinSha took this attack personally and investigated the source of the terrorists.
Since Earth was not yet a member of the Union, and humans had killed a registered guild official, the normal prohibition against using weapons from higher than ten miles over a planet was waived. A MinSha light warship launched several nuclear-tipped missiles into Iran. Then the MinSha landed troops on Iran's borders to glean the war prizes that legal because the terrorists initiated conflict.
While on the planet, humans attacked the MinSha forces and, despite their inferior arms, were able to inflict some casualties on the invaders. Impressed, the MinSha merc commander inquired about these ‘elite human warriors.’ When it was learned they were just Mujahideen warriors, the Buma were excited to realize they’d discovered the 37th merc species of the Union, thereby earning a sizable bonus from the Mercenary Guild for their referral.