Disaster / Destruction
First contact between the TN and HM.
The TN, looking to expand its borders (that they could visit), made contact with the HM by flying into a HM galaxy. They were assimilated, but alerted the rest of the TN about this new threat. These worldships were destroyed afterwards by HF tachyon cannons to deny the HM access to this new, all powerful asset.
This led to billions of deaths, and would take the TN thousands of years to recover. Thus they swore never to attempt visits to the HM ever again, and never did.
The worldship fleet that warped in was, luckily, only a small one in comparison. There were 7 worldships of the fleet. Of course, they did not allow the HM to take them over, and fought back heavily, using the smaller military ships and the worldships themselves. They managed to destroy a large number of HM starships, particularly their larger ships (the TN used their worldships for that). The resulting battle was an intense bloodbath for both sides. The TN ships immediately attempted to warp out, but it did not get enough time to charge up its intergalactic drive for this under HM jamming.
The TN saw the HM use of subspatial starships, and so were inspired to develop some themselves.