Fans of the Black Panther know that he is the king of Wakanda, the highly advanced African nation whose culture revolves around the incredibly strong metal vibranium. Wakanda has been in the public spotlight for quite some time now, but there was a secret part of it that even most Wakandans did not know about until recently.
A space exploration program launched by Wakanda resulted in their territory being expanded not by countries, but by entire planets. This deep dive into the final frontier created a world-spanning empire that would make even the Galactic Empire jealous. And it was not friendly to the Wakandans of Earth.
The Intergalactic Empire of Wakanda first debuted in Marvel Legacy #1 and created by Ta-Nehisi Coates and Daniel Acuna, the Intergalactic Empire of Wakanda was in no way the plan when T'Challa organized the mission. His goal was to learn the origin of the Mena Ngai, the asteroid that brought the vibranium ore to Wakanda in the first place. Chartering its trajectory, this Alpha Flight team, handpicked by T'Challa, was tasked with finding the source of their Sacred Mound. But when it comes to the Marvel Universe (or any comic universe really) going into space is not as assured as one might hope.
While following the asteroid's flight path, the exploration team was sucked into a temporal anomaly that landed them two thousand years in the past. With no way to return to the present, but still in possession of technology more advanced than that of the era, the team of Wakandans decided to build a home for themselves among the stars. Over the next two millennia, their new empire expanded. It ended up encompassing five galaxies, but this expansion did not come without a moral cost.
The Intergalactic Empire of Wakanda forcibly took territory from others. This made enemies of several well-known empires of the Marvel Universe such as the Shi'ar Empire and Rigellians. They even managed to take territory from Klyntar, though not without heavy losses (a given considering who created the symbiotes that inhabited that planet). Those they took captive were forced to work in the vibranium mines, becoming slaves and twisting the message of what Wakanda truly stood for.
The battle with Klyntar is actually where the conflict with T'Challa begins. The then Emperor of the Wakandan Empire had recently come to know N'Jadaka, a warrior and hero to the people of the empire. Fearing that N'Jadaka might one day usurp him, the Emperor sent him and his team on a secret suicide mission to Klyntar. This plan would have succeeded had he not underestimated how much hate the Intergalactic Empire of Wakanda had garnered from the rest of the universe. N'Jadaka's team was murdered, but he bonded with a symbiote who despised the Emperor as much as N'Jadaka did. Together, they returned to the empire and slew the Emperor, claiming the throne for himself.
So when T'Challa arrived from Wakanda Prime (the name for the Earth-based Wakanda), Emperor N'Jadaka saw a threat to his rule. Realistically, even if N'Jadaka was not emperor, the Black Panther would have had a conflict with the Intergalactic Empire of Wakanda anyway. Wakanda was a place of progress and wisdom. To conquer others was not their way and taking slaves to work their vibranium mines was a mockery of everything the Wakandans stood for. So of course the two Wakandan groups would look to each other as adversaries, separated not just by lightyears, but by millennia of cultural shifts that their views on what Wakanda must represent to everyone in the universe.