I believe according to Lore, the Amarr were the first to go into space and develop warp drive technology as well as produce working Jumpgates which they reverse engineered from ancient Takmahl tech-based Jumpgates that were off-lined by the Eve Gate collapse. The Amarr were dedicated to expanding and colonizing space which is why they control the largest area of space.
The Minmatar were the next ones to go into space but hadn’t developed warp drive technology. Instead they developed Acceleration Gate technology which enabled them to find a few ancient Sleeper tech-based Jumpgates that were still operational. That helped them expand to a few other systems. The Minmatar weren’t really interested in expanding and colonizing space and without warp drive technology they were easily enslaved by the Amarr.
The Gallente were the next ones to go into space but hadn’t developed warp drive technology. However they did develop Jumpgates based on ancient Yan Jung technology. They then met the Caldari and shared space travel technology with the Caldari who quickly expanded on it and developed warp drive technology which they shared with the Gallente. The Caldari then developed their own Jumpgate technology based on ancient Talocan technology. They both got into a race to expand and colonize space that started a Century long war between them which stopped their expansion into space.