Tarzan and the Ant-Men, Paperback/Edgar Rice Burroughs

No one had ever crossed the Great thorn Forest until Tarzan of the Apes crashed his plane behind it. Within lay a beautiful country. But in it lived the Alali, strange stone-age giants whose women regarded all men as less than slaves. And beyond the Alali lay the country of the Ant-Men -- little people only eighteen inches tall. There, in Trohanadalmakus, Tarzan was an honored guest--until he was captured by the warriors of Veltopismakus in one of the ant-men's many wars. They had plans for the ape-man. They shrunk Tarzan to their size and set him to work as a quarry slave. Tarzan's only hope is to make a daring escape. But what can an eight inch tall man do?