Quoting Arnold A. Offner’s American Appeasement: United States Foreign Policy and Germany, 1933–1938, pages 22–3, 30–4:

Taking as its starting point the Kellogg‐Briand Pact, the MacDonald plan in Part I allowed any signatory of it and the Kellogg Pact to call for a conference in event of a breach, or threatened breach, of the latter agreement.¹³ The consulting powers—in whose decisions the United States, the United Kingdom, France, [the Third Reich], [Fascist] Italy, [the Empire of] Japan, and the Soviet Union had to concur—were to try to prevent a breach, or determine responsibility if one occurred.

Part II defined troops, a critical point because the French insisted that the […] Schutzstaffel (S.S.) and Sturmabteilung (S.A.) forces be considered regular troops, and limited the number of effectives allowed each European country.

[The Third Reich], having no colonies [yet], could have 200,000 troops on its own soil; France could maintain 200,000 troops at home and 200,000 overseas. Continental soldiers could serve for eight months only, thus converting the Reichswehr into a short‐term army and allowing France the advantage of building a long‐term overseas force. Most important, troop reduction would take place over five years. Meanwhile France would be stronger than [the Third Reich], and the rest of the world would learn whether the Hitler government intended to behave.

Part III dealt with exchange of information; Part IV dealt with prohibitions on chemical, incendiary, and bacterial warfare; and Part V established a Permanent Disarmament Commission, which was to submit at least one report a year and investigate by request, or on its own, alleged treaty infractions. The League Council would review the commission’s reports.

[…]

There was […] surprise and apprehension when the May 11 Leipziger Illustrierte Zeitung carried an article by Neurath declaring that regardless of the Geneva talks [the German Reich] had to rearm on equal footing with other nations. Neurath’s statement, intended to force the British and French to yield to [Berlin’s] demands, had the opposite effect.⁴⁴

The British secretary for war, Lord Douglas Hailsham, threatened military sanctions if [the German Reich] rearmed in violation of the Treaty of Versailles, and the French foreign minister, Joseph Paul‐Boncour, supported the British stand.⁴⁵ Hitler used the opportunity to tell his ministers on May 12 that further disarmament negotiations could lead only to destruction of the [Reichswehr] or blame for Germany if the conference failed.

Both Neurath and General Werner von Blomberg, the minister of war, supported the contention that negotiations no longer would serve any purpose, and the cabinet thereupon announced that the chancellor would respond to recent statements and developments before a special session of the Reichstag on May 17.⁴⁶

In Geneva, Nadolny was so distressed anticipating a truculent address that he rushed to see Hitler and asked him to meet the British halfway by accepting the MacDonald plan as a basis for negotiation. But Hitler only banged his fists on the table, denounced the French, and ended the interview even while Nadolny persisted in his advice.⁴⁷

American diplomats believed the time to act had come. In response to Hull’s inquiry, the chargé in Berlin, George A. Gordon, surmised that Hitler was going to declare that the failure of the powers to grant [the Third Reich] military equality had vitiated the MacDonald plan.

At the same time Davis sent two frantic cables, one urging that Roosevelt speak out before Hitler, and the other proposing that Roosevelt summon Luther to the White House to ask him to urge his country to align itself with the United States, England, and [Fascist] Italy by supporting the MacDonald plan.⁴⁸

Roosevelt meanwhile summoned his advisers—Hull, Phillips, William C. Bullitt, special assistant to Hull, and Louis Howe, Roosevelt’s omnipresent secretary—and they drafted a message to the heads of the fifty‐four states represented in Geneva. Then they turned the draft over to Assistant Secretary Moley with instructions, as he recalled, to “pretty up the language,” and “put the old organ roll into it.”⁴⁹

The President’s May 16 message emphasized the economic burden that heavy arms placed upon nations. The overwhelming majority of peoples, he said, retained excessive armaments because they feared aggression in an age when modern offensive weapons were vastly stronger than defensive ones.

To escape this tragic dilemma by eliminating offensive weapons Roosevelt proposed a four‐step program: acceptance of the MacDonald plan, agreement on time and procedure for steps following it, maintenance of armaments at present levels while carrying out the first and following steps, and a nonaggression pact. He warned that if any strong nation refused to cooperate in the efforts for political and economic peace the world would know whom to blame.⁵⁰

Major newspapers lauded the President’s words. Typically, the New York Times of May 17 praised them as even more bold than any proposal made by Woodrow Wilson and noted that the world eagerly awaited the [Third Reich’s] response. Neurath at once advised Hitler that he could not avoid a careful response to Roosevelt’s message in his scheduled address, but that it would be possible to concur with American principles yet skirt the demand that [the German Reich] not begin to rearm. He sent him a draft of such a reply on the morning of May 17.⁵¹

Hitler, in full [Fascist] uniform, as were the majority of the audience, addressed an excited overflow session of the Reichstag. He spoke softly and swiftly, opening with the usual attack on national passions that clouded judgment and wisdom in 1919 and explaining the [Fascist] revolution as a response to economic conditions and a bulwark against “threatened Communist revolution.”

The Treaty of Versailles, Hitler insisted, granted rights to the conquered as well as the conqueror; [the Third Reich’s] demand for equality was therefore one of “morality, right and reason.” What contribution was the Third Reich willing to make to the present disarmament tangle?

[The Third Reich] would disband its entire military establishment, destroy its few remaining weapons if neighboring countries did the same, and accept the MacDonald plan. [The Third Reich] would have to maintain defense forces as long as other nations did, and not include S.S. and S.A. men as part of the total effectives permitted.

Finally, Hitler in behalf of his country thanked Roosevelt for his message and, for the first and only time during the decade, welcomed the “magnanimous proposal of bringing the United States into European relations as a guarantor of peace.”⁵²

The German Consul in Chicago, Hugo Simon, reported that Hitler’s speech had made an extraordinary impression on everyone, and two days afterward Nadolny stated that his government accepted the MacDonald plan not only as a starting point for discussion but also as a basis for the future agreement, and he withdrew German amendments to the sections on standardization of Continental armies.⁵³

The French were suspicious and perturbed. According to Chargé Marriner in Paris, the brilliant secretary general of the French Foreign Office, Alexis Saint‐Léger Léger, thought Roosevelt’s message an English‐inspired trick to make France’s position at Geneva difficult, and Marriner had to work hard allaying his fears.⁵⁴

The popular political journalist, Andre Géraud (Pertinax), writing in l’Echo de Paris on May 27, considered Roosevelt’s ideas naïve and argued that wars resulted from not defending treaties rather than from defending them. In England the “official mind,” in Chargé Ray Atherton’s words, would not accept Hitler’s speech as a declaration of policy unless [the Third Reich] without further delay standardized its army.

In Berlin Chargé Gordon, recognizing that Hitler had taken a statesmanlike and conciliatory position, suspected it might well be a ruse to gain time to secure control at home, and then the world might see what [Fascists] privately had described to Gordon as “the real Hitler—the advocate of the doctrine of force, as laid down in his book My Struggle.”⁵⁵

Davis did not share his colleagues’ skepticism or fear. He thought [the Third Reich] more conciliatory than ever and believed the “profound effect” of Roosevelt’s speech had induced [the Third Reich] to retreat “from an almost impossible position.”

It was now time, he said, for the United States to make “some move,” perhaps a meeting of the heads of state of Europe’s major powers. Roosevelt and Hull agreed, and instructed Davis to expand upon Roosevelt’s May 16 message by way of a public response to the proposals Henderson had been discussing with American diplomats in Geneva since March.⁵⁶