Wikipedia's article on horizontal integration defines the strategy but gives no historical origin date, citing only modern mergers (Heinz-Kraft 2015, Marriott-Starwood 2015, AB InBev-SABMiller 2016, Disney-21st Century Fox 2019) as examples. The strategy is far older; Standard Oil's 1870s-1880s consolidation of refining capacity is widely cited elsewhere as a classic 19th-century instance, but no source found in this research names a coining date or first-use event for the term or the strategy.
What would resolve this A business-history or economics source documenting when horizontal integration first emerged as a named, recognized strategy, or one explicitly stating the concept has no single origin because it describes a strategy practiced informally long before it was named.
OpenWikipedia, Horizontal Integration