Foreign hops

From the middle of the 19th century, increasingly large quantities of foreign hops were used by UK brewers. Why? The UK simply couldn't produce enough hops to meet demand.

The result was that the UK imported hops from pretty much everywhere that grew them. But not all hops were created equal. And those from certain countries were far more valued. Though for different reasons.

German hops, in particular from Bavaria and Württemberg, were valued because of their flavour. While American hops were liked for their economy. That is, because they were higher in alpha acid fewer needed to be used.

The majority of English brewers employ very few foreign hops when those of their own country are good and may be purchased at a reasonable price. Foreign hops, such as those imported from Bavaria, Bohemia, America, Australia, and the Colonies, yield a decided harsh bitter flavour as already referred to, and although foreign beer consumers are used to, and like it, the public of this country would discard beer thus bittered. Usually, brewers employ one-fourth American hops for the production of mild ales, or even a larger percentage of other growths, but usually the limit does not reach or even exceed half foreign and half English. Bavarian hops, and especially those of the Halledau and Wurtemburg growths, are extremely good, both for copper and dry hopping all classes of beer. They impart a rich nutty flavour of their own.
Thatcher, Frank, A Treatise of Practical Brewing and Malting (The Country Brewers' Gazette, London, 1907), page 235.

As always, there's a warning about overuse of American hops, on account of their horrible flavour.

Californian and other hops coming from the Pacific States must be sparingly used, as although the black currant flavour and aroma is not so strong in these hops as it used to be, yet it can be easily detected if an excessive amount of such material is employed.
Thatcher, Frank, A Treatise of Practical Brewing and Malting (The Country Brewers' Gazette, London, 1907), pages 235 - 236.

While German hops were OK to use for dry-hopping.

Bavarians, Wurtemburgs, Halledaus, etc., also impart a rich flavour to beers, which is, however, entirely devoid of the characteristic delicate flavour usual to Worcester and Kent hops, although they may be employed for dry hopping in the cask during warm weather with the best possible iesults on account of their antiseptic constituents, and they are often the means of preventing beers developing premature acidity.
Thatcher, Frank, A Treatise of Practical Brewing and Malting (The Country Brewers' Gazette, London, 1907), pages 236 - 237.

Though note that they didn't rate the flavour as highly as the best-quality English hops.