The claim that Hitler allegedly "broke" the Munich agreement - which has been covered already - is an bald-faced lie. Yet sometimes historians who wish to accuse Hitler of breaking a promise don't mention the Munich agreement
per se, instead they allude to a conciliatory "agreement" signed between Hitler and Chamberlain at Munich on September 30th 1938, which stated to the effect that as representatives of Germany and Great Britain, they would consult each other on any further "questions that may concern our two countries". These "questions" were left undefined, and it's by no means clear that Czecho-Slovakia (now hyphenated) was any of Britain's concern, nor was it clear that this last minute agreement suggested by Chamberlain, was anything more than a piece of paper which served the purpose of declaring good-will in a gentlemanly manner between the two countries. Nonetheless, Hitler is accused of "breaking" this "agreement" (which was too short and vague to really be deserving of such a title). This has already been shown to be nonsense, but it must be reiterated, and will be momentarily...
It's also said, particularly at the time when Hitler turned the Czech state into a protectorate after the secession of Slovakia on March 14, that Hitler had "broken his promise at Munich that the Sudetenland would be his last territorial demand in Europe". This was also a lie, one that was kept out of the eye of the Anglophone public around the world and remains largely in-tact today.
The reality is that the British knew full well that Czechia was going to be brought further into the German orbit, and that she'd probably become a protectorate. They knew, because they had initiated it by suggesting that Hacha go to Berlin:
On March 14, in the morning hours, Slovakia and Carpatho-Ukraine placed themselves under the protection of the German Reich as independent states, following declarations of independence and decisions of their new governments. HITLER assumed the protection of Slovakia, not Ruthenia, to which Hungary also laid claim. Still on March 14, Hungary invaded Ruthenia after a 12-hour ultimatum to Prague. In view of this worsening situation of the breakup of Czecho-Slovakia, the British Ambassador in Berlin, Nevile HENDERSON, on March 14, 1939, urgently suggested to the Czech Envoy in Berlin, MASTNY, that he see to it that the Czech Foreign Minister, CHVALKOWSKY, come immediately to Berlin and discuss the situation with HITLER. The British Ambassador in Prague, NEWTON, supported this. HACHAS's later visit to Berlin with his Foreign Minister was thus at British suggestion, not initiated by HITLER.
Moreover, even before HACHA's arrival in Berlin, the German Secretary of State in the Foreign Office, Ernst VON WEIZSÄCKER - father of the later Federal President - had asked HENDERSON how the British Government would behave if HACHA, as was to be expected, placed the rest of Czechoslovakia under a German protectorate. HENDERSON, therefore, knowing the German intention of the future of Bohemia and Moravia, immediately informed London of it and was authorized by the British Foreign Secretary, HALIFAX, to declare that Great Britain had no desire to interfere in matters which directly concerned other countries. HENDERSON assured the Germans that London would not interfere in their Czech policy.
Rolf Kosiek und Olaf Rose (ed.), Der Grosse Wendig: Richtigstellungen zur Zeitgeschichte: Band 1 (Tübingen: Grabert-Verlag, 2006), Pp. 566-567; David L. Hoggan, Der Erzwungene Krieg: Die Ursachen und Urheber des Zweiten Weltkriegs (Tübingen: Grabert-Verlag, Vierzehnte Auflage 1990), Pp. 336. In English: David L. Hoggan, The Forced War: When Peaceful Revision Failed (Institute for Historical Review, 1989), Pp. 248.
This was also confirmed by Francis Neilson as I previously quoted in this thread:
The report that Hitler had acted entirely on his own in this matter is quite untrue. The British documents show that Sir Neville Henderson was informed of everything that took place. His dispatch to. Halifax in Documents on British Foreign Policy 1919-1939, Third Series, Volume IV (1951), No. 256, is conclusive proof of the correct diplomatic procedure. There is, also, in the same volume the dispatch of Mr. Newton from Prague to the British Foreign Office (No. 262). We learn from them:
. . . The Czecho-Slovak President declared that in order to serve this purpose, and in order to secure final pacification, he placed the destiny of the Czech people and country with confidence in the hands of the Führer of the German Reich. The Führer accepted this declaration and expressed his determination to take the Czech people under the protection of the German Reich and to guarantee to it an autonomous development of its national life in accordance with its particular characteristics.
Francis Neilson, Some Political Issues in the Background of World War II, The American Journal of Economics and Sociology, Vol. 18, No. 4 (Jul., 1959), Pp. 384.
A few things are made clear from this.
1. The gentleman's agreement signed by Hitler Chamberlain - even if applicable - for Germany and Britain to "consult each other" was not violated due to the fact that Halifax on part of Great Britain had reupdated any British interest in the Czech affair because it wasn't her concern.
2. The agreement couldn't have been violated because the British government had been consulted, if not integrally involved in bringing the Hacha-Hitler conference about, therefore they had been consulted.
3. The British couldn't pretend that it was unlikely that Czechia would be absorbed by Germany.
Chamberlain on March 15, 1939, initially confirmed the line Halifax had laid down, by justifying the German "invasion" of Czechia, effectively saying that it was none of Britain's business because the Czech state no longer existed in it's previous form:
Chamberlain declared in the House of Commons on 15 March 1939 there has been no breach of the Munich Convention. The the British Government is no longer bound by its commitment to Czechoslovakia because "the state whose borders we intended to guarantee from within and thus came to an end".
Annelies von Ribbentrop, Verschwörung gegen den Frieden (Druffel Verlag, Zweite erweiterte Auflage 1963) Pp. 304.
And on March 17th in a speech at Birmingham Chamberlain admitted that there was nothing Britain could've done anyway:
. . . Nothing that we could have done, nothing that France could have done, or Russia could have done could possibly have saved Czechoslovakia from invasion and destruction. Even if we had subsequently gone to war to punish Germany for her actions, and if after the frightful losses which would have been inflicted upon all partakers in the war we had been victorious in the end, never could we have reconstructed Czechoslovakia as she was framed by the Treaty of Versailles. . .
Neville Chamberlain, March 17, 1939. See: Neilson, op cit., p. 384.
The point of this post was just to compile some of the information already posted, along with some confirmatory new information.