Winter War
Another proposal was a massive air strike with Turkish co-operation against the Caucasus oil fields.
The British, for their part, wanted to block the flow of iron ore from Swedish mines to Germany as the Swedes supplied up to 40 per cent of Germany's iron demand. The matter was raised by British Admiral Reginald Plunkett on 18 September 1939, and the next day Winston Churchill brought up the subject in the Chamberlain War Cabinet. On 11 December, Churchill opined that the British should gain a foothold in Scandinavia with the objective to help the Finns, but without a war with the Soviet Union. Because of the heavy German reliance on Northern Sweden's iron ore, Hitler had made it clear to the Swedish government in December that any Allied troops on Swedish soil would immediately provoke a German invasion.
On 19 December, French Prime Minister Édouard Daladier introduced his plan to the General Staff and the War Cabinet. In his plan, Daladier created linkage between the war in Finland and the iron ore in Sweden. There was a danger of Finland's possible fall under Soviet hegemony. In turn, Nazi Germany could occupy both Norway and Sweden. These two powers could divide Scandinavia between them, as they had already done with Poland. The main motivation of the French and the British was to reduce German war-making ability.
The Military Co-ordination Committee met on 20 December in London, and two days later the French plan was put forward. The Anglo-French Supreme War Council elected to send notes to Norway and Sweden on 27 December, urging the Norwegians and Swedes to help Finland and offer the Allies their support. Norway and Sweden rejected the offer on 5 January 1940. The Allies came up with a new plan, in which they would demand that Norway and Sweden give them right of passage by citing a League of Nations resolution as justification. The expedition troops would disembark at the Norwegian port of Narvik and proceed by rail toward Finland, passing through the Swedish ore fields on the way. This demand was sent to Norway and Sweden on 6 January, but it was likewise rejected six days later.
Stymied but not yet dissuaded from the possibility of action, the Allies formulated a final plan on 29 January. First, the Finns would make a formal request for assistance. Then, the Allies would ask Norway and Sweden for permission to move the "volunteers" across their territory. Finally, to protect the supply line from German actions, the Allies would send units ashore at Namsos, Bergen, and Trondheim. The operation would have required 100,000 British and 35,000 French soldiers with naval and air support. The supply convoys would sail on 12 March and the landings would begin on 20 March. The end of the war on 13 March cancelled Franco-British plans to send troops to Finland through Northern Scandinavia.

Aftermath and casualties: 

Finland: The 105-day war had a profound and depressing effect in Finland. Meaningful international support was minimal and arrived late, and the German blockade had prevented most armament shipments. The 15-month period between the Winter War and Operation Barbarossa, part of which was the Continuation War, was later called the Interim Peace. After the end of the war, the situation of the Finnish Army on the Karelian Isthmus became a subject of debate in Finland. Orders had already been issued to prepare a retreat to the next line of defence in the Taipale sector. Estimates of how long the Red Army could have been delayed by retreat-and-stand operations varied from a few days to a few weeks, or to a couple of months at most.
Immediately after the war, Helsinki officially announced 19,576 dead. According to revised estimates in 2005 by Finnish historians, 25,904 people died or went missing and 43,557 were wounded on the Finnish side during the war. Finnish and Russian researchers have estimated that there were 800–1,100 Finnish prisoners of war, of whom between 10 and 20 per cent died. The Soviet Union repatriated 847 Finns after the War. Air raids killed 957 civilians. Between 20 and 30 tanks were destroyed and 62 aircraft were lost. Also, Finland had to cede all ships of the Finnish Ladoga Naval Detachment to the Soviet Union by virtue of the Moscow Peace Treaty.
During the Interim Peace, Finland aimed to improve its defensive capabilities and conducted negotiations with Sweden on a military alliance, but negotiations ended once it became clear that both Germany and the Soviet Union opposed such an alliance. On 31 July 1940, German Chancellor Adolf Hitler gave the order to plan an assault on the Soviet Union and so Germany had to reassess its position regarding Finland. Until then, Germany had rejected Finnish appeals to purchase arms. However, the prospect of an invasion of the Soviet Union reversed the policy. In August, the secret sale of weapons to Finland was permitted.
Karelian evacuees established an interest group, the Finnish Karelian League, to defend Karelian rights and interests and to find a way to return ceded regions of Karelia to Finland. Finland wished to re-enter the war mainly because of the Soviet invasion of Finland during the Winter War, which had taken place after Finland had failed by relying on the League of Nations and on Nordic neutrality. Finland aimed primarily to reverse its territorial losses from the Moscow Peace Treaty and, depending on the success of the German invasion of the Soviet Union, possibly to expand its borders, especially into East Karelia. Some right-wing groups, such as the Academic Karelia Society, supported a Greater Finland ideology. The Continuation War began in June 1941 and led to Finnish participation in the Siege of Leningrad as well as the Finnish occupation of East Karelia.

Soviet Union: The Soviet General Staff Supreme Command (Stavka) met in April 1940, reviewed the lessons of the Finnish campaign and recommended reforms. The role of frontline political commissars was reduced, and old-fashioned ranks and forms of discipline were reintroduced. Clothing, equipment and tactics for winter operations were improved. Not all of the reforms had been completed when Germans initiated Operation Barbarossa 14 months later.
Between the Winter War and perestroika in the late 1980s, Soviet historiography relied solely on Molotov's speeches on the Winter War. In his radio speech of 29 November 1939, Molotov argued that the Soviet Union had tried to negotiate guarantees of security for Leningrad for two months. The Finns had taken a hostile stance to "please foreign imperialists". Finland had undertaken military provocation, and the Soviet Union could no longer abide by the non-aggression pacts. According to Molotov, the Soviet Union did not want to occupy or annex Finland, but the goal was purely to secure Leningrad.
The official Soviet figure, with reference to the command of the Leningrad Military District, was published at a session of the Supreme Soviet on 26 March 1940, with 48,475 dead and 158,863 sick and wounded. More recent Russian estimates vary: in 1990, Mikhail Semiryaga claimed 53,522 dead, and N. I. Baryshnikov, 53,500. In 1997, Grigoriy Krivosheyev claimed 126,875 dead and missing and total casualties of 391,783, with 188,671 wounded. In 1991, Yuri Kilin claimed 63,990 dead and total casualties of 271,528. In 2007, he revised the estimate of dead to 134,000 and in 2012, he updated the estimate to 138,533. In 2013, Pavel Petrov stated that the Russian State Military Archive has a database confirming 167,976 killed or missing along with the soldiers' names, dates of birth and ranks.
There were 5,572 Soviet prisoners of war in Finland. After the Winter War, the Soviet prisoners were returned to the USSR in accordance with the Moscow Peace Treaty. Of these, 450 were released, 4,354 were sentenced to imprisonment in labour camps ranging from 3 to 10 years and 414 were exposed to be "active in traitorous activities while in captivity", with 334 criminal cases being transferred to the Supreme Court of the Soviet Union; 232 of those cases ended in a death penalty.
Between 1,200 and 3,543 Soviet tanks were destroyed. The official figure was 611 tank casualties, but Yuri Kilin found a note received by the head of the Soviet General Staff, Boris Shaposhnikov, reporting 3,543 tank casualties and 316 tanks destroyed. According to Finnish historian Ohto Manninen, the 7th Soviet Army lost 1,244 tanks during the breakthrough battles of the Mannerheim Line in mid-winter. In the immediate aftermath of the war, the Finnish estimate of the number of lost Soviet tanks was 1,000 to 1,200. The Soviet Air Forces lost around 1,000 aircraft, but fewer than half of them were combat casualties. According to Carl Fredrik Geust, based on the studies of Soviet air force units, Finnish anti-aircraft units shot down 119 and Finnish fighter pilots 131 Soviet aircraft, though all Soviet aircraft losses had been more than 900.

Germany: The Winter War was a political success for the Germans.