Why does Steinbeck compare the farming industry in California to the Roman Empire?

This quote is from chapter 19 and it pretty much explains it,

"Now farming became industry, and the owners followed Rome, although they did not know it. They imported slaves, although they did not call them slaves: Chinese, Japanese, Mexicans, Filipinos. They ice on rice and beans, the business men said. They don’t need much. They couldn’t know what to do with good wages. Why, look how they live. Why, look what they eat. And if they get funny--deport them."