Before I start talking about branch plants in Canada in the 1920’s, it’s important that you know what a branch plant is. The definition provided by http://www.timetoast.com/timelines/81853 is: [A] branch plant is a system introduced by Americans, [that] involves American manufacturing and commercial firms that were located in Canada to avoid the import tariffs that was part of [the] Nation’s Policy.This means that the profits made by these branch plants usually were obtained by the United States’ companies.
There were mixed feelings from Canadians about these U.S. branch plants. Some Canadians felt that American investment was good for Canada. These people felt that the American capital would help Canada develop into a strong economic nation. However, other Canadians felt that too much American investment in Canada would result in the States gaining control of the nation’s economy (called “Americanization of the Canadian economy”). These Canadians worried that too many decisions about the Canadian branches were made by the States. Lastly, there was a group of Canadians who felt that the government should allow American branch plants, but they should limit the amount of American investment in Canada.
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Branch plants, relating to the “roar” of the ‘20’s, was a good thing because it provided employment for returning war soldiers. Therefore, I believe that branch plants contributed to the “roar” of the 1920’s.
Canada’s economy was considered well-off in the 1920’s. However, the government paid little attention to the economy’s boom, as they were more concerned about paying off the debts from World War I.
Interestingly, another political party formed during the 1920’s — the Progressive Party. This party was formed by farmers that felt threatened by the lower wheat prices.
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Canada was relatively well-off during the 1920’s, therefore I believe these political matters contributed to the “roar” because the good economy allowed people to party and have fun, which is what the roar is referring to.
Surrealism and art deco were two art movements that started in the 1920’s.
The Surrealism movement began right after World War I. Surrealists commenced many techniques such as automatic drawing — developed by André Masson, automatic painting, decalcomania, grattage, frottage, parsemage, and fumage. These techniques became significant parts of the Surrealist practice.

(Above) This was a surrealism piece of art titled Plastron et fourchette produced by Jean Arp in 1922.
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Art Deco was a major style that began in Europe in the early 1920’s, but didn’t catch on in the United States until around 1928. It is a decorative arts that also affected architecture. This style of art is characterized by its bold use of zigzag and stepped forms, sweeping curves, chevron patterns, and sunburst motif on various materials including aluminium, stainless steel, lacquer, inlaid wood, sharkskin, and zebraskin. This design was a conscious split from the past — before the war — and it was created to commemorate the new technologies (ie. electricity, gas powered vehicles)

(Above) This is a set of art deco-style bookmarks created by artist Junichi Nakahara.
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The 1920’s “roared” with the introduction of different art styles. Art diverted from the classical “it must look real and perfect” style to the new and — in some cases — more abstract modernized art.
Advertising took a completely different turn in the 1920’s. A good example of this is through Coca-Cola’s advertisements.
When Coca-Cola was first introduced in the 1880’s, it was marketed as a medicine. Advertisements claimed it cured headaches, “revived and sustained” a person, and the Coca plant was a valuable Brain Tonic that could cure many things.

By the 1920’s, Coca-Cola was no longer advertised as a medicinal drink, but instead as a refreshing “fun food”. Instead of advertising using words, they relied heavily on bright and consumer attracting colors with little words. The advertisement (shown below) shows the drastic change in advertising.
The bright colors used in the advertisement tells the consumer that Coca-Cola is fun and enjoyable. The colors also attract consumers and the logo makes the product easier for the consumer to remember.

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The 1920’s “roared” even in terms of advertisement. The advertisements were fun, happy, and bright — just like the 1920’s!