Miért voltak a nyugat-európai hatalmak olyan durván intoleránsak a kisebbségeikkel szemben Magyarországhoz képest az 1789-1939 közötti korszakban?

In July 1849, the Hungarian Revolutionary Parliament proclaimed and enacted the WORLD's FIRST laws on ethnic and minority rights. It gave minorities the freedom to use their mothertongue at local administration, at tribunals, in schools, in community life and even within the national guard of non-Magyar councils. However these laws were overturned after the united Russian and Austrian armies crushed the Hungarian Revolution of 1848.

After the Kingdom of Hungary reached the Compromise with the Habsburg Dynasty in 1867 (Ausgleich), one of the first acts of the restored Hungarian Parliament was to pass a Law on Nationalities (Act Number XLIV of 1868).

The situation of minorities in Hungary was not even comparable to the contemporary pre WW1 Europe. Other highly multiethnic /multinational countries were: France Russia and UK.

See the multi-national UK:

The situation of Scottish Irish and Welsh people in "Britain" during the English hegemony is well known. They utmost forgot their original language,only English language cultural educational institutions existed. The only language was English in judiciary procedures and in offices and public administrations. In Wales Welsh children were beaten by their teachers if they spoke Welsh among each others. This was the infamous “Welsh Not” policy... See: [link]

The contemporary Irish question and tensions are well documented. The situation of Ireland was even a more brutal and bloody story. It was not a real "United" Kingdom, it was rather a greater England.

See the multiethnic France:

In the era of the Great French revolution, only 25% of the population of Kingdom of France could speak the French language as mothertongue. In 1870, France was still similar-degree multi-ethnic state as Hungary, only 50% of the population of France spoke the French language as mothertongue. The other half of the population spoke Occitan, Breton, Provençal, Catalan, Corsican, Alsatian, West Flemish, Lorraine Franconian, Gallo, Picard or Ch’timi and Arpitan etc... Many minority languages were closer to Spanish languages or Italian language than French) French governments banned minority language schools, minority language newspapers minority theaters. They banned the usage of minority languages in offices , public administration, and judiciary procedures. The ratio of french mothertongue increased from 50% to 91% during the 1870-1910 period!!!

The situation in German Empire was well known (Polish territories and Sorbs)

Just look some Eastern countries in the oreintal so-called Eurasian (aka. Orthodox) civilization :

The legal system of pre-WW1 Kingom of Serbia did not know minority rights.

Also, the legal system of pre-WW1 Kingdom of Romania did not know minority rights, morover, Kingdom of Romania applied strong anti-Semitic disciminative laws against Jewish people, which was similar to Tzarist Russia. Read about it here: [link]

Slavery disappeared during the high medieval period on Western Christian European soil, however it existed in Romanian territories until the mid 19th century! The Gypsy slavery and slave markets were abolished only in 1852!!! (Gypsies of Romania had similar status like blacks in USA before the civil war) See: [link] and see: [link]

Just examine the high contrast between Kingdom of Hungary and contemporary pre WW1-era Europe:

The so-called "Magyarization" fantasy was not so harsh as the contemporary western European situation, because the minorities were defended by minority rights and laws. Contemporary Western European legal systems did not know the minority rights, therefore they loudly and proudly covered up their minorities. 1.Were there state sponsored minority schools in Western European countries? NO. 2. How many official languages existed in Western-European states? Only 1 official language! 3. Could minorities use their languages in the offices of public administration in self-governments , in tribunals in Western Europe? No, they couldn't. 4. Did the minorities have own fractions and political parties in the western European parliaments ? No, no they hadn't. 5. What about newspapers of ethnic minorities in Western Europe? They did not exist in the West.... We can continue these things to the infinity.

The Austro-Hungarian compromise and its supporting liberal parliamentary parties remained bitterly unpopular among the ethnic Hungarian voters, and the continuous successes of these pro-compromise liberal parties in the Hungarian parliamentary elections caused long lasting frustration for Hungarians. The ethnic minorities had the key role in the political maintenance of the compromise in Hungary, because they were able to vote the pro-compromise liberal parties into the position of the majority/ruling parties of the Hungarian parliament. The pro-compromise liberal parties were the most popular among ethnic minority voters, however i.e. the Slovak, Serb and Romanian minority parties remained unpopular among their own ethnic minority voters. The coalitions of Hungarian nationalist parties – which were supported by the overwhelming majority of ethnic Hungarian voters – always remained in the opposition, with the exception of the 1906–1910 period, where the Hungarian-supported nationalist parties were able to form a government.[48]