A: Pay attention to when the cartoon was made: 1939. Since a few years before that it was already visible Germany was preparing for war. Since at least 1933 Germans were openly rearming themselves and reenforcing their military. Thus when the artist draws the cartoon the Second World War was at least imminent, if it hadn't started alrady -- we don't know the exact month of publication. So the point the artist's trying to make is that the Treaty of Versailles was responsible for his present scenario by portraying that at the same time the Treaty established peace (the dove in the sky), it created the prospect of a new war in the horizon (skeleton below).
B: It is consensus between historians that the Treaty of Versailles had, at least, a lot of responsability for the Second World War. The treaty did not actually end what caused the First World War, that is, competition between European powers for territories outside Europe, and it created a series of sanctions on Germany that would be politically instrumentalized into feelings of resentment against anyone not-German.
C: The Treaty established Germany as the guilty for the First World War obligating payment of a great sum of money to the rest of the Allied Powers. This put German in a violent economical crisis. It also demanded Germany restored Alsacy-Lorraine as French territory -- a territory German had won in the Franco-German war (1870). The economical crisis added to the resentment caused by the loss of Alsacy-Lorraine to the French made Germans fertile to extreme ideas like Nazism.