“It was his introduction to the reign of primitive law and he met the introduction halfway" ,means?

This Chapter One quote is found directly after Buck has been beaten repeatedly by one of his captors. With each blow he receives, Buck fights back, until finally.... he is knocked senseless. In this new world, Buck must come to terms with “the reign of primitive law,” in which force, not morality, takes power. In this place, a man with a club (or even a more powerful dog) can abuse the weak. In this particular scene, Buck is made slave to the man who beats him. Over time, however, he will use their rules to become master in his own right.