Read this novel circa late 1950s. Plot as follows from vague and imperfect memory. Earth is expanding into near stellar neighborhood. Finds planet that once held a now-vanished civilization, but which left behind remnants of very high tech science. Learns that a galaxy-conquering empire is expanding toward Earth.
Develops newly found science into weapons with the help of cat-like people in order to resist the invasion. Inflicts great casualties on empire but loses against overwhelming forces, but with almost no casualties because of force shields based on new science.
Earth leader is brought before galactic emperor, who is surprised to learn of low human casualties. Earth leader gains one concession from galactic emperor in return for technology secrets: a single seat in the galactic empire’s senate/parliament. Human plan is to use that one seat as a platform to spread human ideals to galaxy-wide peoples.
