so he can say "trade intensified" while when what actually happened is that the presence of trade (= useful outlet for additional e.g., crops) changed incentives, and then farmers etc choose differently. 
In a micro setting that change happens gradually, but from the purview of a historian a millennium later, the [add foreign trade] and [harder/better farm work] is going to look like they occurred at the same time. 

Perhaps that granularity/zoom-in vs zoom-out is why presents the causality upside down?

denlillaapan

what, the farmers weren't running their oxen hard enough, getting as much crop yield as they were later? Non-optimized?

I don't know what he would think the story is but my sense is that saliency of optimized effort is the answer.

Absent trade, working harder just gets you more of the same shit you produce for yourself. That's going to face diminishing marginal returns. So, you'll settle into more of an effort minimized production structure.

Once trade goods become available, extra effort pays off with new goods that provide greater marginal values. So, you work harder and innovate and reoptimize your practices.

BooksAndArticles

econ

Capitalism Book Club #2: CHAPTER 1, and the Historian Returns

> what, the farmers weren't running their oxen hard enough, getting as much crop yield as they were later? Non-optimized?

I don't know what he would think the story is but my sense is that saliency of optimized effort is the answer.

Absent trade, working harder just gets you more of the same shit you produce for yourself. That's going to face diminishing marginal returns. So, you'll settle into more of an effort minimized production structure.

Once trade goods become available, extra effort pays off with new goods that provide greater marginal values. So, you work harder and innovate and reoptimize your practices.