On the 12th August, 1939, Hitler had a conversation with Ciano and the defendant Ribbentrop at Obersalzberg. He said then:
" Generally speaking, the best thing to happen would be for the neutrals to be liquidated one after the other. The process could be carried out more easily if on every occasion one partner of the Axis covered the other while it was dealing with the uncertain neutral. Italy might well regard Yugoslavia as a neutral of this kind."
This observation was made only two months after Hitler had given assurances to Yugoslavia that he would regard her frontier as final and inviolable. On the occasion of the visit to Germany of the Prince Regent of Yugoslavia on 1st June, 1939, Hitler had said in a public speech:
" The firmly established reliable relationship of Germany to Yugoslavia now that owing to historical events we have become neighbours with common boundaries fixed for all time, will not only guarantee lasting peace between our two peoples and countries, but can also represent an element of calm to our nerve-racked continent. This peace is the goal of all who are disposed to perform really constructive work."
On the 6th October, 1939, Germany repeated these assurances to Yugoslavia, after Hitler and Ribbentrop had unsuccessfully tried to persuade Italy to enter the war on the side of Germany by attacking Yugoslavia. On the 28th October, 1940, Italy invaded Greece, but the military operations met with no success. In November Hitler wrote to Mussolini with regard to the invasion of Greece, and the extension of the war in the Balkans, and pointed out that no military operations could take place in the Balkans before the following March, and therefore Yugoslavia must if at all possible be won over by other means, and in other ways. But on the 12th November 1940, Hitler issued a directive for the prosecution of the war, and it included the words:
" The Balkans: The Commander-in-Chief of the Army will make preparations for occupying the Greek mainland north of the Aegean Sea, in case of need entering through Bulgaria."
On the 13th December he issued a directive concerning the operation " Marita," the code name for the invasion of Greece, in which he stated:
" 1. The result of ,the battles in Albania is not yet decisive. Because of a dangerous situation in Albania, it is doubly necessary that the British endeavour be foiled to create air bases under the protection of a Balkan front, which would be dangerous above all to Italy as to the Roumanian oilfields.
2. My plan therefore is (a) to form a slowly increasing task force in Southern Roumania within the next month, (b) after the setting in of favourable weather, probably in March, to send a task force for the occupation of the Aegean north coast by way of Bulgaria and if necessary to occupy the entire Greek mainland."
On the 20th January, 1941, at a meeting between Hitler and Mussolini, at which the defendants Ribbentrop, Keitel, Jodl and others were present, Hitler stated:
" The massing of troops in Roumania serves a threefold purpose.
(a) An operation against Greece;
(b) Protection of Bulgaria against Russia and Turkey;
(c) Safeguarding the guarantee to Roumania....
It is desirable that this deployment be completed without interference from the enemy. Therefore, disclose the game as late as possible. The tendency will be to cross the Danube at the last possible moment, and to line up for attack at the earliest possible moment."
On the 19th February, 1941, an OKW directive re the operation "Marita" stated:
" On the 18th February the Fuehrer made the following decision regarding the carrying out of Operation Marita: the following dates are envisaged: Commencement of building bridge, 28th February: Crossing of the Danube, 2nd March."
On the 3rd March, 1941, British troops landed in Greece to assist the Greeks to resist the Italians; and on the 18th March, at a meeting between Hitler and the defendant Raeder, at which the defendants Keitel and Jodl were also present, the defendant Raeder asked for confirmation that the "whole of Greece will have to be occupied, even in the event of a peaceful settlement," to which Hitler replied, "The complete occupation is a prerequisite of any settlement."
On the 25th March, on the occasion of the adherence of Yugoslavia to the Tripartite Pact at a meeting in Vienna, the defendant Ribbentrop, on behalf of the German Government, confirmed the determination of Germany to respect the sovereignty and territorial integrity of Yugoslavia at all times. On the 26th March the Yugoslav Ministers, who had adhered to the Tripartite Pact, were removed from office by a coup d'etat in Belgrade on their return from Vienna, and the new Government repudiated the Pact. Thereupon on 27th March, at a conference in Berlin with the High Command at which the defendants Goering, Keitel and Jodl were present, and the defendant Ribbentrop part of the time, Hitler stated that Yugoslavia was an uncertain factor in regard to the contemplated attack on Greece, and even more so with regard to the attack upon Russia which was to be conducted later on. Hitler announced that he was determined, without waiting for possible loyalty declarations of the new Government to make all preparations in order to destroy Yugoslavia militarily and as a national unit. He stated that he would act with " unmerciful harshness."
On the 6th April German forces invaded Greece and Yugoslavia without warning, and Belgrade was bombed by the Luftwaffe. So swift was this particular invasion that there had not been time to establish any "incidents" as a usual preliminary, or to find and publish any adequate "political" explanations. As the attack was starting on the 6th April Hitler proclaimed to the German people that this attack was necessary because the British forces in Greece (who were helping the Greeks to defend themselves against the Italians) represented a British attempt to extend the war to the Balkans.
It is clear from this narrative that aggressive war against Greece and Yugoslavia had long been in contemplation, certainly as early as August of 1939. The fact that Great Britain had come to the assistance of the Greeks, and might thereafter be in a position to inflict great damage upon German interests was made the occasion for the occupation of both countries.
Sources: The Avalon Project