There were several border conflicts between Colombia and Peru in the early part of the 20th century, and in 1922, their governments signed the Salomón-Lozano Treaty to try and resolve these conflicts. As part of this treaty, the border town Leticia and its surrounding area were ceded from Peru to Colombia, giving Colombia access to the Amazon River.
On 1 September 1932, business leaders from the Peruvian rubber and sugar industries who had lost land when the area was given to Colombia organised an armed takeover of Leticia. At first, the Peruvian government did not recognise the military takeover but Peru's President Luis Sánchez Cerro decided to resist a Colombian re-occupation. The Peruvian army occupied Leticia, resulting in an armed conflict between the two nations. After months of diplomatic wrangling, the governments accepted mediation by the League of Nations, and their representatives presented their cases before the League's Council. A provisional peace agreement, signed by both parties in May 1933, provided for the League to assume control of the disputed territory while bilateral negotiations proceeded. In May 1934, a final peace agreement was signed, resulting in the return of Leticia to Colombia, a formal apology from Peru for the 1932 invasion, demilitarization of the area around Leticia, free navigation on the Amazon and Putumayo Rivers, and a pledge of non-aggression.

Background Manchurian Crisis: The depression hit Japan hard. Both China and the US put up Tariffs against Japanese goods. The Japanese domestic industry was threatened with complete collapse. At the same time the militaries influenced the politicians strongly. This combination led to the attack on Manchuria. This Chinese district had a lot of the raw material Japan needed...
The Mukden Incident, also known as the "Manchurian Crisis " or the "Far Eastern Crisis", was one of the League's major setbacks and acted as the catalyst for Japan's withdrawal from the organization. Under the terms of an agreed lease, the Japanese government had the right to station its troops in the area around the South Manchurian Railway, a major trade route between the two countries, in the Chinese region of Manchuria. In September 1931, a section of the railway was lightly damaged by officers and troops of the Japanese Kwantung Army as a pretext for an invasion of Manchuria. The Japanese army, however, claimed that Chinese soldiers had sabotaged the railway and in apparent retaliation (acting contrary to the civilian government's orders) occupied the entire region of Manchuria. They renamed the area Manchukuo, and on 9 March 1932 set up a puppet government with Pu Yi, the former emperor of China, as its executive head.
Internationally, this new country was recognized only by the governments of Italy and Germany; the rest of the world still considered Manchuria legally part of China. In 1932, Japanese air and sea forces bombarded the Chinese city of Shanghai, sparking the January 28 Incident.
The League of Nations agreed to a request for help from the Chinese government, but the long voyage by ship delayed League officials from investigating the matter. When they arrived, the officials were confronted with Chinese assertions that the Japanese had invaded unlawfully, while the Japanese claimed they were acting to keep peace in the area. Despite Japan's high standing in the League, the subsequent Lytton Report declared Japan to be the aggressor and demanded Manchuria be returned to the Chinese. Before the report could be voted on by the Assembly, Japan announced its intention to push further into China. The report passed 42-1 in the Assembly in 1933 (only Japan voted against), but instead of withdrawing its troops from China, Japan withdrew its membership from the League .
According to the Covenant, the League should have responded by placing economic sanctions on Japan, or gathered an army and declared war. Neither of these actions was undertaken, however. The threat of economic sanctions would have been almost useless because the United States was not a League member. Any economic sanctions the League had placed on its member states would have been ineffective, as a country barred from trading with other member states could simply turn and trade with the United States. The League could have assembled an army, but major powers like Britain and France were too preoccupied with their own affairs, such as keeping control of their extensive colonies, especially after the turmoil of World War I. Japan was therefore left in control of Manchuria, until the Soviet Union's Red Army took over the area and returned it to China at the end of World War II.

Rhineland, Austria, Sudetenland, Czechoslovakia, Memel, Danzig, Poland...

On 17 July 1936, the Spanish Army launched a coup d'état, leading to a prolonged armed conflict between Spanish Republicans (the leftist government of Spain) and the Nationalists (conservative, anti-communist rebels who included most officers of the Spanish Army). Alvarez del Vayo, the Spanish Minister of Foreign Affairs, appealed to the League in September 1936 for arms to defend its territorial integrity and political independence. The League members, however, would not intervene in the Spanish Civil War nor prevent foreign intervention in the conflict. Hitler and Mussolini continued to aid General Francisco Franco’s Nationalist insurrectionists, and the Soviet Union aided the Spanish Republic. In February 1937, the League did launch a ban on the intervention of foreign national volunteers.

Following a long record of instigating localised conflicts throughout the 1930s, Japan began a full scale invasion of China on 7 July 1937. On 12 September, the Chinese representative, Wellington Koo, appealed to the League for an international intervention. Western countries were sympathetic to the Chinese in their struggle against Japan, particularly in their stubborn defence of Shanghai, a city with a substantial number of foreigners. However, the League was unable to provide any practical measure other than a final statement that gave China "spiritual support." On 4 October, the League adjourned and turned the case over to the Nine Power Treaty Conference...