Mobilization
A unique solution of perpetuations was instituted, and mobilization during the Second World War did not repeat Sir Sam Hughes' model, which has been described by historians as being more closely akin to ancient Scottish clans assembling for battle than a modern, industrialized nation preparing for war.

"Colonials" served under British command though, perhaps owing to the limited autonomy granted to the Dominions regarding their respective mobilizations, the Dominions eventually compelled the British government to overrule the objections of some British commanders and let the Dominion forces serve together instead of being distributed amongst various British divisions. The "colonials" would go on to be acknowledged by both the British and German high commands as being elite British units. In May 1918, when command of the Australian Corps passed from William Birdwood to John Monash, it became the first British Empire formation commanded totally free of British officers.
On May 23, 1915, Italy entered World War I on the Allied side. Despite being the weakest of the big four Allied powers, the Italians soon managed to populate its army from 560 to 693 infantry battalions in 1916; the army had grown in size from 1 million to 1.5 million soldiers. On August 17, 1916, Romania entered the war on the Allied side, mobilizing an army of 23 divisions. Romania was quickly defeated however by Germany, Austria-Hungary, and Bulgaria. Bulgaria went so far as to ultimately mobilize 1.2 million men, more than a quarter of its population of 4.3 million people, a greater share of its population than any other country during the war.
The production of supplies gradually increased throughout the war. In Russia, the expansion of industry allowed a 2,000 percent increase in the production of artillery shells – by November 1915, over 1,512,000 artillery shells were being produced per month. In France, a massive mobilization by the female population to work in factories allowed the rate of shell production to reach 100,000 shells a day by 1915.
Both sides also began drawing on larger numbers of soldiers. The British Secretary of State for War, Lord Kitchener, appealed for hundreds of thousands of soldiers, which was met with an enthusiastic response. 30 new British divisions were created. The response by volunteers allowed the British to put off the introduction of conscription until 1916. New Zealand followed suit, with Canada also eventually introducing conscription with the Military Service Act in 1917.
On April 6, 1917, the United States entered the war on the Allied side. At the entrance, the U.S. only could mobilize its army of 107,641 soldiers, ranked only seventeenth in size worldwide at the time. The United States Navy quickly mobilized, adding 5 dreadnoughts to the Allied navy. However, conscription quickly ensued. By March 1918, 318,000 U.S. soldiers had been mobilized to France. Eventually, by October 1918, a force of  2 million U.S. soldiers joined in the war effort.

Mobilization in World War II: Poland partly mobilized its troops on August 24, 1939, and fully mobilized on August 30, 1939, following the increased confrontations with Germany since March 1939. On September 1, 1939 Germany invaded Poland, which prompted both France and Britain to declare war on Germany. However, they were slow to mobilize, and by the time Poland had been overrun by the Axis powers, only minor operations had been carried out by the French at the Saar River.
Canada actually carried out a partial mobilization on August 25, 1939, in anticipation of the growing diplomatic crisis. On September 1, 1939, the Canadian Active Service Force (a corps-sized force of two divisions) was mobilized even though war was not declared by Canada until September 10, 1939. Only one division went overseas in December 1939, and the government hoped to follow a "limited liability" war policy. When France was invaded in May 1940, the Canadian government realized that would not be possible and mobilized three additional divisions, beginning their overseas employment in August 1940 with the dispatch of the 2nd Canadian Division (some units of which were deployed to Iceland and Newfoundland for garrison duty before moving to the UK). Canada also enacted the National Resources Mobilization Act in 1940, which among other things compelled men to serve in the military, though conscripts mobilized under the NRMA did not serve overseas until 1944. Conscripts did, however, serve in the Aleutian Islands Campaign in 1943 though the anticipated Japanese defense never materialized due to the evacuation of the enemy garrison before the landings. Service in the Aleutians was not considered "overseas" as technically the islands were part of North America.
The United Kingdom mobilized 22% of its total population for direct military service, more than any other nation in the WWII era.
Up to 34 million soldiers served in the Red Army during World War II, representing the largest military force in world history.

Post–World War II: Volodymyr Zelenskyy, the President of Ukraine, signed a decree on February 24, 2022 on the general mobilization of the population in the 2022 Russian invasion of Ukraine.
Conscripts and reservists were called up over the next 90 days to "ensure the defense of the state, maintaining combat and mobilization readiness". Men between the ages of 18 and 60 were prohibited from leaving the country.
Vladimir Putin, the President of Russia, announced a partial mobilization on 21 September 2022 of existing reservists, most particularly those that have military experience. According to claims of the Russian defence minister Sergei Shoigu, 300,000 reservists would be mobilized.

Economic mobilization: Economic mobilization is the preparation of resources for usage in a national emergency by carrying out changes in the organization of the national economy.
It is reorganizing the functioning of the national economy to use resources most effectively in support of the total war effort. Typically, the available resources and productive capabilities of each nation determined the degree and intensity of economic mobilization. Thus, effectively mobilizing economic resources to support the war effort is a complex process, requiring superior coordination and productive capability on a national scale. Importantly, some scholars have argued that such large scale mobilization of society and its resources for the purposes of warfare have the effect of aiding in state building. Herbst argues that the demands of reacting to an external aggressor provides a strong enough impetus to force structural changes and also forge a common national identity.

See also: Civil conscription
Combat readiness
Impressment
Levée en masse
War economy

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References: 

Further reading: United States Department of the Army (1955): History of Military Mobilization in the United States Army, 1775-1945 (online)

External links: 
Online version of The army and economic mobilization (1959), by R. Elberton Smith
Swiss government PDF on mobilization (German)
mobilization procedure of the Austrian Federal Army (in German)
Economic mobilization since World War II
Mobilisation