Assess the value of these three sources to an historian studying the aims of Stalin's foreign policy in the years 1929 to 1939.

(One third of full answer)Source 3, an unpublished speech to the Politburo, is of the most value to an historian studying the aims of Stalin's foreign policy from 1929 to 1939. In terms of provenance, the fact that the speech was not published and that only a select group of party members were in attendance suggests its purpose was to persuade them rather than for use as propaganda material. Moreover, because the speech is Stalin's own, its content is more likely to reflect the true aims of his foreign policy; this further increases its value. In the speech itself, Stalin's overall argument is that the outcome of a pact with Germany would be positive for the USSR. Its main result would be an "inevitable" war in Poland that would not initially involve the USSR but instead would allow it to "make a successful entry later". Such emphasis on delaying military intervention is valuable because it illustrates Stalin's focus on resolving internal issues rather than creating external ones. Indeed, after the recent economic slowdown and the Purge of the Military (1937), which implicated 50% of all officer corps, the USSR certainly needed more time before it could engage in armed conflict. Stalin then goes on to explain that the resultant destruction of Poland, the Anglo-French bloc and the German Reich "is in the interests of the USSR". The tone here conveys his enthusiasm and underlines that an aim of Stalin's defensive foreign policy was to allow the rest of Europe to self-destruct. This is clearly justified given that after WW1, the countries that fared the worst, such as France, witnessed a Communist resurgence. If such an event were to reoccur, the prospect of spreading Communism abroad would dramatically increase.
That said, there are some limitations that slightly detract from the source's value. The main issue is that the speech was made in August 1939 and, because it does not explicitly refer to events before this point, it is perhaps less valuable in the context of the entire 1929-1939 period. By virtue of this provenance, the source's content seems to suggest that Stalin's foreign policy was wholly defensive and that "remaining on the sidelines" was the key priority. In reality, Stalin also aimed to promote the USSR as a defender of democracy over fascism, as evidenced by his intervention in the Spanish Civil War (July 1936). Despite this omission, the speech highlights a number of other foreign policy aims between 1929 and 1939. Taking this into account, the source is still the most valuable of the three.