Where, exactly, was the "Sudetenland?"

The Sudetenland (Czech and Slovak: Sudety, Polish: Kraj Sudetów) is the German name (used in English in the first half of the 20th century) to refer to those northern, southwest, and western areas of Czechoslovakia which were inhabited mostly by German speakers, specifically the border districts of Bohemia, Moravia, and those parts of Silesia located within Czechoslovakia.

This is straight from the wiki.

The "Sudetenland" has two meanings, it might be used as a term for border regions of todays Czech Republic inhabited by (not only) German minority - and in this meaning it is mostly used, but strictly said, Sudetenland was only a region in northern Moravia (eastern part of the Czech Republic). The Germans that lived in these areas and in many "language insels" came typicaly in 16th c. (Among scholars no one (except Bertold Bretholz) seriously believed that there was any continuity between the theutonic tribes of the Roman era and Germans later recorded in the medieval written sources.) Yet, German and Flemish enterpreneurs brought an important know-how in 13th c. and were an important minority, esp. in the cities. The problem is that until 19th century, when the modern nationalism was established, prevailed the oppinion that all inhabitants of Bohemia are Bohemians, i. e. inhabitants of the land, rather than Czechs, or Germans. Even later, once the national identities were well defined and had also strong elites, the identity of the great numbers of people was fluid and might have changed.

This question is extremely interesting to me. It's been part of an ancestry research project of mine. My paternal family comes from the Sudetenland, but sadly, with the recent passing of my dad late last year, the last first hand source in my family is also silent.

I will try and fill in this answer over time, which might be a bit unusual of an approach. But I have 1500 pages of books and documents that I need to go through to give a proper answer that isn't just lines on maps. Besides if nobody is interested I don't have to worry about adding reams of info later on. ;)

I'm not even going to bother with Wikipedia (English or German editions) so see at the bottom for sources.

To begin, Sudetengermans originated in ancient Bohemian and Markomannic tribes mentioned all the way back by Tacitus. Together with their Slavic neighbours, Czech tribes, they ended up inside the Habsburg empire in around 1526 (5, page 7).

The term Sudetengerman ist actually very young and was coined early in the 20th century to align with Alpine Germans and Carpathian Germans, i.e as another German group living in mountainous regions. In this case the Sudeten mountains in the northern ranges of the then Habsburg empire. (5, page 14)

The term was collectively used for Germans from Bohemia, Moravia and Austrian-Silesia. When the Habsburg empire disintegrated after World War 1 and Czechoslovakia was founded, the Sudetengermans found themselves inside a new Slavic country. Despite the Wilson doctrine, any attempts at autonomy, self-determination or integration with Germany failed. (5, page 14)

Union with Austria would have been geographically absurd (look at a map), though not strictly impossible, as there are and have been precedents.

Strictly speaking, they wouldn't have belonged to Germany either! No more than Austria or Switzerland do. But, just like Yugoslavia, you knew this wasn't going to end well.

Oh, and that's the German-speaking view. In all fairness, the history from the Czech view varies: from their POV large areas had been left ununhabited when entire tribes moved westward during the migration periods. However it's not debated that in these specific areas near the Sudeten ranges, German-speaking ethnicity was in the majority.

As is too common, who was the oppressor and who the victim changed with who was in control of the overall area. With the German-Austrian Habsburgers ruling, the Sudetengermans were top dog. When that ended, the Czechs became the Bad Guys, cracking down (sometimes violently) on any secession attempts, or even increased autonomy.

To answer the main question from the OP: as so often the was no fixed border. With ethnical lines far more fluent than drawn on a map, where a German majority became parity with Czechs and then changed to Czech majority wasn't discrete - and probably depended on who did the counting!

With the perceived or real oppression experienced it's no wonder that the Sudetengermans welcomed the invasion of the Hitler's forces with open arms. Nor is it a wonder, after the horrors of Nazi occupation, the Czechs wanted the Germans gone, who were guilty by association at best and perpetrators at worst.

However it shouldn't be forgotten that with 2-3 million Sudetengermans being kicked out, the approach of the Communists rulers who took over in the late 1940s was to simply uproot about 1.9 million Czechs and simply tell them to now live in the vacated areas. Or else (1, page 15).

That was still "simpler" than what happened in Poland, where the entire country was shifted westward. Stalin typically held on to what he had opportunistically gained in 1939 while still allied with Germany, so instead of giving it back he handed Silesia to Poland, kicking out millions of Poles who then had to pack up and head westwards.

Some of my sources (not counting family papers and documents):

1. Als die Deutschen weg waren (When the Germans were gone), by a
   consortium of German, Polish and Czech authors
2. Historische Ansichten vom Sudetenland (Historical sights and insights of the Sudetenland), by Heinz Csallner
3. Sudetenland in 144 Bildern (Sudetenland in 144 images), by Erhard J. Knobloch
4. Paurisch, Handbuch der Gablonzer Mundart (Paurish, dictionary of the dialect of the Gablonz/Jablonec area), by Hans-Joachim Hübner and Kurt Fischer
5. Typisch Sudetendeutsch (Typical Sudetengerman), by Viktor Aschenbrenner

I live in Plzeň and I am located in Plzeň and I assure you that no sensible force has ever considered Plzeň to be a town in the Sudetenland.

The Sudetenland has two approximately but not completely equivalent definitions:

• the mountain ranges along the border of the Czech lands (you may see the nearly circular border of Bohemia from the satellites – which disagrees with astronauts' proclamations that they can't see any border from the outer space – and the Bohemian basin could have been created by a meteor 2 billion years ago) – by the way, in the Czech geography, they have never been considered a single mountain range, and we interpret them as a collection of 10 or so mountain ranges.

• the very precise territory that belonged to Czechoslovakia up to the Munich Treaty but was annexed by the Third Reich for the period Fall 1938 - March 1939.

Some seven centuries ago, in order for them to improve the domestic economy, the Czech kings cleverly started to invite ethnic German settlers to the Sudeten mountain range. They brought some sophisticated agricultural know-how – and later some industry, primarily light one – and they seemed more capable of flourishing in the mountains than the Czechs who, as farmers, seemed to be confined to the lowlands. After some time, the percentage of the ethnic Germans in the mountain regions of the Czech lands increased substantially.

Note that the Sudetenland or its Czech translation, Sudety, was formally banned in Czechoslovakia when the war ended in 1945. Everyone understood it and no one has ever run into trouble while using it but it was "politically incorrect". When needed, the term "pohraničí" or "příhraničí" (the borderland) was understood to be the synonym.

Plzeň just doesn't belong into the Sudetenland according to neither definition. First, Plzeň isn't really a town in the mountains. The center of the town is at 300 meters above the sea level. The town is surrounded by very moderate hills that we call "Plzeňská pahorkatina" – the "Pilsner Hilly Area" although this translation is mine and I am not sure whether anyone uses it in English. It's nothing like the mountains in the Northern Bohemia etc.

Second, Plzeň remained in the Second Republic of Czecho-Slovakia after the Munich Treaty. The border between Czecho-Slovakia and the Sudetenland part of the Third Reich went a mile from the city limits, in the Western direction away from the town. This had important implications, of course. The Škoda Works remained a Czecho-Slovak company for those six months or so.

When the Protectorate of Bohemia and Moravia was declared in March 1939, all the factories on the Czech territory began to work for the Third Reich and the Škoda Works was an important producer of German tanks and other things. They played a nontrivial role in the German successful excursions to the Western Europe.

Also, I must mention that historically, Plzeň was never considered a city with a dominant German minority. The German minority has been important for many centuries – perhaps 1/5 by population and 1/4 by importance some 100 years ago. There was a German-language theater here, and so on. But the city was always ruled primarily by ethnic Czechs. For centuries, trade with the Germans in Regensburg and Nuremberg was very important for Plzeň so the town was "integrated" to the broader German economy just like it is today and the co-existence between the Czechs and Germans was OK. But there were never any doubts about "which ethnic group is mainly in charge". It was the Czechs.

All these facts have visible consequences for the present era. Many of the Sudetenland towns were repopulated and this had significant costs. But Plzeň remained similar to what it used to be, with a healthy economy and no important ethnic scars.

These three maps clearly outline, in varying level of detail, the portions of Czechoslovakia that were annexed by Nazi Germany in 1938. As the definition of "Sudetenland" has almost no meaning apart from this annexation, they comprise a de facto meaning of the term.

As illustrated below, the city of Plzen was just outside the boundaries of Sudetenland as defined above.