What did Americans mean when they spoke of "the trusts?'

"Trust" had a particular legal and institutional meaning.  When two or more businesses turned over control of their investments and operations to a third party, a "trustee" or a "board of trustees," they were creating "a trust."  For the most part, trusts of this sort were illegal in business according to common law and, after 1890, by statutory law.

One example: at one point in its history, John D. Rockefeller's Standard Oil Company was a "trust" in which firms once in competition with one another turned over control to a trustee, Rockefeller, so that all would be operated in harmony with one another.   This kind of "trust " proved unwieldy (and illegal), and it seldom lasted except to give a simple name to the complex process, "the rise of big business."

The word trust, or the phrase "the trusts," also had a broader meaning in the early twentieth century.  Americans applied this term to large business firms.   They especially applied the term "trust" to firms that had grown large and displaced smaller firms as they grew.

A department store thus might be a "trust" because it was a large firm, employing many people,  and took business from small retailers, displacing them.

For what reasons did big businesses grow, prosper, or die?