Henlein attended business school in Gablonz (Jablonec nad Nisou) and in World War I entered the Austro-Hungarian Army as a military volunteer (Kriegsfreiwilliger), assigned to the k.u.k.

He was severely wounded, then captured by the Italians, and spent the rest of the war as a POW on Asinara Island, where he studied the history of the German Turner (gymnastics) movement of Friedrich Ludwig Jahn.

[4] Knowing that the Czechoslovak authorities were about to ban the two main völkisch parties in the Sudetenland for treason, on 1 October 1933, Henlein founded the Sudetendeutsche Heimatfront ("Sudeten German Home Front", SHF).

Henlein's association with the Catholic Kameradschaftsbund, which followed the teachings of Austrian philosopher Othmar Spann, allowed him to argue that his movement was not a continuation of the banned parties.

[5] American historian Gerhard Weinberg described Henlein as "...a thirty-five year-old veteran of the war who had achieved prominence in a racist athletic organization in the Sudeten area.

[10] Cornwall wrote that "...there slowly developed a chasm between Henlein's self-perception as a Sudeten Führer and the reality of a man who lacked both charisma and political acumen.

[22] The main right-wing Czech parties favored preserving Czechoslovakia as a single state, and Henlein's talks with them quickly floundered over this issue.

[24] In May 1936, Czechoslovak Prime Minister Milan Hodža declared in a speech: "The government would take care that Henlein achieved no success, and it was confident that the SdP would then split up into various factions that could then be more easily handed".

"It may well be that Germany has designs on Czechoslovakia in any event," wrote the Permanent Undersecretary of the Foreign Office, Sir Robert Vansittart after meeting him, "but it is quite certain that at present the Czechoslovak government are providing them with ... a first-class pretext".

One Foreign Office official wrote in April 1937 when a journalist from The News Chronicle presented evidence that Germany was financing the SdP that the documents "do not really tell us anything new".

[32] However, Henlein's demands served to distract attention from the February reforms and allowed him to once again present the Sudeten Germans as being "oppressed" by Beneš, supposedly denying them the right to their own "racial identity".

[32] Henlein did not become a declared follower of Adolf Hitler until 1937, after the pro-German camp within the SdP represented by Karl Hermann Frank emerged victorious.

In October 1937 the Czechoslovak authorities were tipped off (possibly by the German secret service) about the homosexuality of his close ally Heinz Rutha, who was imprisoned on charges that he had had sexual relations with young men active in the SdP.

Unknown to Henlein, on 5 November 1937 at the conference in Berlin recorded in the Hossbach Memorandum, Hitler declared that he was planning to attack Austria and Czechoslovakia in the very near future.

[33] British historian Richard Overy noted that in the Hossbach memorandum Hitler said nothing about Czechoslovakia's treatment of the Sudeten Germans as a reason for war, instead saying that Germany was falling behind in the arms race with Britain and France, and so needed to conquer Czechoslovakia to exploit its resources, industries and people to take the lead in the arms race and to provide for economic autarky to make Germany immune to a British blockade.

[37] Hitler believed that Italy could hold both Britain and France in check and that there was no danger that a German attack on Czechoslovakia would cause a wider war.

[40] On 5 April 1938, Henlein told a Hungarian diplomat that "whatever the Czech government might offer, he would always raise still higher demands...he wanted to sabotage an understanding by all means".

[37] The apparent moderation of the Karlsbad programme, demanding only autonomy, was intended to make Czechoslovakia appear intransigent, "forcing" Germany to invade.

[43] Hitler wanted the demand for German regiments to be the ninth point in the Karlsbad programme, but Henlein persuaded him that it was too inflammatory and too likely to alienate public opinion abroad.

[53] Starting on 12 May 1938, Henlein visited London and impressed almost everyone he met as an apparently reasonable, mild-mannered man full of genial charm, who just wanted autonomy for his people.

[54] Henlein promoted the idea that he only wanted a "fair deal" for the Sudeten and claimed that he opposed the Sudetenland joining Germany, noting that after the Anschluss Austrian Nazis were pushed aside by the Germans.

[57] In the May 1938 local elections in the Sudetenland, the SdP candidates for town and village councils won 87%–90% of the votes cast, indicating that a majority of the Sudeten Germans were behind Henlein.

[58] Frustrated with the unwillingness of Henlein and Hodža to talk, in the summer of 1938 the British government, believing that both parties wanted an agreement, sent an intermediary to Czechoslovakia they thought might be able to break the deadlock.

[64] In early September 1938, President Beneš announced the "Fourth Plan" for constitutional change to make Czechoslovakia into a federation, which did not meet all of the demands of the Karlsbad programme, but did grant autonomy to the Sudetenland.

On 9 September 1938, Benito Mussolini formally endorsed all eight points of the Karlsbad programme and denounced Czechoslovakia as "tainted" by its alliances with France and the Soviet Union.

[67] Greek historian Aristotle Kallis wrote: "The problem [for Hitler] was that the British government took the irredentist alibi of Nazi expansionism quite seriously, eager to make concessions on these lines, without realising that no territorial offer on ethnic grounds would never satisfy the geographical prerequisites of the fascist 'new order'".

[71] On 28 September 1938, Hitler told French ambassador André François-Poncet that he was willing to attend a conference in Munich to discuss a peaceful solution to the crisis, with Mussolini as a mediator.

[77] Henlein attempted to place his long-term followers in key positions in his Reichsgau and, starting in the spring of 1939, became locked into a battle over patronage with Reinhard Heydrich.

[10] Heydrich let the accused go on trial in early 1940 rather than taking them into "protective custody" when the courts heard lurid stories of how in the 1930s the SdP leaders had engaged in homosexual orgies.

[16] In March 1940, at a party rally in Hohenelbe (modern Vrchlabí, Czech Republic), Henlein formally denouncing Rutha—the best man at his wedding in 1926—as a homosexual "pervert", and embraced Heydrich's Großdeutschland nationalism, asserting that Sudeten Germans were no different from the Reichdeutsch.