Keep in mind, Adam Smith was an enlightenment-era philosopher. It would have been strange had the founding father of capitalism not written about his own time period... Adam Smith drew largely from Hume and Hobbes and viewed capitalism as a way to maintain man's greed. Adam Smith also viewed capitalism as the natural development which would follow the mercantilist trading regime in Europe.

Marx's theory draws largely from the philosopher Hegel- and Marx employs a Dialectic Materialist analysis to argue that the history of man is a history of class conflict.

There are other accounts of the development of capitalism. But personally, I find the institutionalist argument as put forth by Karl Polanyi (a Democratic Socialist) the most persuasive. I can't do it justice in a reddit comment, but it examines the "transformation" into capitalism as it manifested through institutions and state intervention. If you're interested in how capitalism was formed and its implications, I highly recommend The Great Transformation).