The League's Role in Peacekeeping

Successfully solved disputes:

The dispute between Weimar Germany and Poland over Upper Silesia (1920–21):

Upper Silesia was an economically significant region with a mixed population of Germans and Poles, resulting in Germany and Poland contending for control over the region.

To avoid an escalation in the dispute, the League of Nations appointed a commission to oversee a plebiscite and ensure that it was conducted fairly. On March 20, 1921, the population of Upper Silesia was given the choice to vote whether the region should belong to Germany or Poland. 

The final result showed a narrow majority in favour of being under German rule, but with significant areas that voted heavily for being under Polish rule. As a result, the League of Nations proposed that Upper Silesia be partitioned; with the east being awarded to Poland and the West to Germany.  This solution was accepted by both Weimar Germany and Poland. 

The dispute between Sweden and Finland over the Aaland Lands (1920–21):

Both countries claimed that the Aaland lands were their territory. Finland claimed it was theirs as it was geographically closer and belonged to Finland since independence in 1917. Sweden claimed it was theirs as 90% of the population was Swedish. 

The League of Nations appointed a commission to investigate the Åland Islands dispute. Thorough research was carried out, and consultations were conducted with both Finland and Sweden, as well as with the Åland Islanders themselves.

In 1920, the League issued the Åland Report, which proposed that the Åland Islands remain part of Finland but be granted extensive autonomy and self-governance. It also included guarantees for the preservation of the Swedish language, culture, and local traditions.

Both Finland and Sweden accepted the recommendations of the Åland Report and an international treaty known as the Åland Convention was negotiated and signed in 1921, formalising the terms of autonomy for the Åland Islands within Finland.

The 'Stray Dog' or 'Petrich' Incident between Bulgaria and Greece (1925)

In October 1925, a Greek soldier pursuing a stray dog accidentally crossed the Bulgarian border near the village of Petrich. Bulgarian border guards, mistaking the soldier's actions for an intrusion, fired warning shots and detained the Greek soldier. Some casualties were reported on both sides. Greece demanded Bulgaria punish those responsible, issue an official apology, and pay two million French francs as compensation to the families of the victims. When they failed to do so, Greece invaded Bulgaria and occupied the town of Petrich. Fighting between Greek and Bulgarian forces ensued, and Bulgaria asked the League of Nations to intervene. 

The League's commission conducted an impartial investigation into the incident and proposed a settlement which redefined the border, and both countries agreed to withdraw their troops. Greece was told to pay £45,000 in compensation. If the rulings were not followed, the League threatened to impose economic sanctions.

Unsuccessfully solved disputes:

The dispute between Poland and Lithuania over the city of Vilna (1919–20):

Following the break-up of the Russian and German Empires after World War One, the city of Vilna, a historically multicultural center with a sizable Polish and Jewish population, became a focal point of contention between Poland and Lithuania. In April 1919, Polish forces seized control of Vilna, which had been claimed by Lithuania as its capital since independence from Russia in 1918 due to historical and cultural ties to the region. However, Poland refused to recognize Lithuania's sovereignty over Vilna.

In response, the League of Nations intervened and appointed a commission to investigate the situation and propose a solution. A report issued in July 1920 recommended that Vilna should be placed under an international administration until a permanent resolution could be reached. However, this proposal was rejected by Poland and the Vilna Incident remained unresolved. Britain and France (or any other nation) did not send troops to enforce the League's decision. Vilna became the capital of the newly established Second Polish Republic, while Lithuania refused to recognize Polish sovereignty.

The Corfu Crisis between Italy and Greece (1925)

While investigating a border dispute between Greece and Albania, an Italian General, Enrico Tellini, and several of his men were killed. Mussolini blamed the Greeks and issued an ultimatum to Greece, demanding immediate payment of reparations and the punishment of the perpetrators. Italy also demanded that Greek officials be removed from the region and that Italy be granted control over certain strategic areas of Greek territory. When Greece refused, Mussolini ordered soldiers to occupy Corfu until Greece apologised and paid compensation. 

Mussolini refused to cooperate with the League and announced he would withdraw Italy from the League if it interfered. Mussolini asked the Conference of Ambassadors to resolve the Corfu Crisis in 1923 and Britain and France gave into his demand to resolve the issue outside of the League. The Conference of Ambassadors ordered Italy to withdraw from Corfu and ordered Greece to pay an indemnity as a 'gesture of goodwill' despite there being no evidence that Greece was involved in the killings. 

• This was the first major test for the League of Nations, and the League's failure to settle it fairly showed that it was weak, and could not settle disputes in which a larger power (e.g. Italy) was the aggressor and confronted a small country (e.g. Greece).

Additionally... the League was unable to get members to agree to limit the size of their armed forces.