Bankruptcies, destruction and reduced diversity in the 20th century.
The Bavarian Reinheitsgebot is extended in 1906 to all the German empire, despite the warnings and protests of the German brewers. Beers brewed only with barley malt, water and hops are now authorized to be sold inside the German Empire. This authoritarian measure will cause the extinction of many Northern German regional specialties such as spiced beer, the cherry beer, or the Steinbier. This depletion will pave a motorway in Germany to the lager beer type, mostly brewed in Southern Germany. The Bavarian brewers share a same brewing tradition with their colleagues in Bohemia and Moravia (today Tchequia and Slovakia).
In 1880, there were about 2,400 breweries operating in the United States covering most styles of classic brewing. Today, there are only 375 breweries. The change is dated of 1919. The Volstead Act and the 18th Amendment to the Constitution are introduced during prohibition. During this period, small breweries have thrown in the towel and larger have survived by producing malts and non-alcoholic fake-beers.
The temperance organizations, when they do not advocate the total prohibition of alcohol as in the United States, see in the beer a lesser damage compared to distilled spirits (gin, rum, eau-de-vie, etc..), strong wines, liquors, and other absinthes. Provided that beer is a healthy drink, and remains a low alcohol beverage. This results in official tax rates by which each national administration classifies all its beers according to the sole criterion of the alcoholic volume.
Finally, the temperance campaigns and the State policies which aim to control and tax the beer industry not only converge, but favor the larger breweries. These latter pursue a growth by absorption or disappearance of local brewers as competitors. The standardized beer produced on a large scale cross the objectives of a tax administration that does not want to check each beer-tavern or farm-brewery, each small town brewery. The state guidelines are more easily discussed and negotiated between a central government administration and a small number of operators of big national breweries.
Two World wars ravaged the European continent. Each time, the brewers came out ruined : in wartime, the grains are the food of men and animals. Only large beer plants can be converted to make the bread for soldiers. Each time, the breweries are plundered: copper tanks, lead and tin are used to make weapons and shells. At the end of the Second World War, the number of breweries fall dramatically in all countries, even in Germany and Belgium. The movements of capital and the industrial concentration will eclipse the last independent regional brewers in the 1980s. Even in Germany, mergers accelerate.
In Eastern Europe after le Second World War, the economic centralization makes disappear the private breweries. The only remaining beer brands are brewed by standardized methods in State breweries. A special mention must be made for a beer speciality of East Berlin that survives: the Berliner weisse, malt barley + raw wheat with additional lactic fermentation. Paradoxically, the reunification of Germany signs the disappearance of this original beer in the brewing European landscape.
A revival occurs in the 80s to fight against excessive standardization of European beers. The initiative comes from the genuine lovers of ales, concerned about the loss of their local beer in the pubs of UK, replaced by a bland lager to the continental way. The movement is started and crossed the Channel. It takes the form of pub-breweries and micro-breweries able to brew most typed beers sold on site or very locally.
Apparent return to the brewing traditions of the 19th century? Not at all. Miniaturized and cheaper, the technology of the major breweries is now available since the 80's for small and even tiny brewing installations. Even an amateur can steer a miniature automated brewery.
Is it a pledge of original beers? No. It all depends on the imagination and experience of the brewer, the dynamism of the "owner-innkeeper", and the tastes of its customers (more or less prone to taste new beers with unknown tastes). As new places for brewing, the micro-breweries often replicate the range of the industrial beers (blond, amber, dark, wheat beer).
Second barrier: the directives governing the brewery and defining the "beer" at European level are still more sterilizing and reductive than the addition of the former national regulations on beer.
EBC beer definition (EU Directive 92/83/EEC, article 2) = « EBC beer definition (EU Directive 92/83/EEC, article 2) = « For the purposes of this Directive, the term 'beer' covers any product falling within CN code 2203 or any product containing a mixture of beer with non-alcoholic drinks falling within CN code 2206, in either case with an actual alcoholic strength by volume exceeding 0,5 % vol. Establishment of the duty. » 
We note that these European definitions, modeled after international customs nomenclatures, are becoming narrower. For comparison, the definition of beer in France a century ago said : « Beer is a beverage obtained by alcoholic fermentation of a wort made with hops and pure barley malt or combined ... with malt from other grains » (Décrets du 28 juillet 1908). This text, replacing the law edicted in 1816 and very controversial by brewers, laid the foundations of modern brewery in France, according to P. Voluer (De Céréales et d'eau. La brasserie française. Terrain n° 13 1989). The technical role let to malts from others grains than barley must be noticed. This old French legislation stayed attached to the European tradition of malting.
 The CN code 2203 is given by a Customs classification harmonized at European level. It says : The term "beer" is reserved for the beverage obtained by alcoholic fermentation of a wort prepared from malt grain, raw materials from grains, dietary sugars, hops, substances imparting of bitterness from the hops, and drinking water.
Therefore, a beer must be brewed at least with malt and hops. No hops, no beer. No malt, no beer ! The only way to saccharify the starch would be the malting, according to these restrictive legal definitions. A traditional rice beer (brewed by amylolytic enzymes) from China, or a manioc beer from Brazil (same process) must be imported in Europe with a label "wine" and not "beer" to comply with these absurd customs regulations. The same restrictions are issued by the U.S. Customs Code. These national regulations are all harmonized on similar codifications and definitions to be compatible with each others. Another example of a legal and administrative aberrant definition : " A vehicle is equipped with a gasoline or diesel motor ". Who could then design an electric motor car! The same absurdity is involved in the official beer definition.