I would identify three principal events in the period 1800–1850 as expressions of American nationalism: the Louisiana Purchase, the War of 1812, and the Mexican-American War.

The interesting fact is that none of these actions were universally endorsed by the US public—and they were perhaps not even endorsed by the majority. The Purchase of the Louisiana territory under Jefferson and the Mexican War under the Polk administration both added enormous swaths of territory to the US. The latter especially was criticized by the political opposition as being simply a cover for the agenda of extending slavery to the added territories. But whatever the real purpose, these actions and the War of 1812 (which resulted in the end of British interference in internal US affairs and the end of their desultory and cynical attempts to stir up Native Americans against the settlers) expanded and secured the sovereignty of the United States. This encouraged more immigration from Europe, which then strengthened the economy, supplying more laborers for the growing industrial system in the northern states. Though they unfortunately and tragically did extend slavery, the acquisitions of the Louisiana territory and Texas increased the cotton production of the US, which was a principal export in the growing economic power of the country.

Ultimately, nationalism became a force more directly rooted in the population as a whole and not just of the presidents, their administrations, and Congress. New immigrants from Europe, as well as people whose families had long been in the US, knew that America, despite its severe flaws, represented democratic values and an improvement (at least for those of European descent) over the relative lack of freedom and equality in the Old World. This was a driving force in the wish of most Americans to keep the Union together at all costs. They realized that if the US were to collapse through secession, the cause of world democracy would suffer a defeat. And the fact that the Union was maintained, through the long period of sectional dispute and the Civil War it culminated in, resulted in the economy almost ironically being strengthened further and the US becoming an economic powerhouse as it entered its Gilded Age in the latter half of the nineteenth century.

In the early 1800s, a strong feeling of nationalism swept across the United States. This led the United States to stand up to other countries that were pushing us around. Two of these countries were Britain and France. We decided to stop all trade in 1807 with the passage of the Embargo Act. However, this proved to be disastrous for us because we depended on trade. We then passed the Non-Intercourse Act that banned trade with Britain and France since these were the countries that were interfering with our trade. However, that action also failed because we traded so much with these countries. A group of young senators, called War Hawks, advocated for war against Britain because they were the biggest offenders in terms of interfering with our trade. The War Hawks displayed a strong sense of nationalism because they believed no country should push us around. 

After the War of 1812 with Britain, the spirit of nationalism remained strong. Henry Clay developed the American System. This placed protective tariffs on imports, created a national bank, and led to the building of roads and canals. These actions helped our economy grow. We entered an Era of Good Feelings where there was little political dissent because we had only one political party. We were able to accomplish a great deal during this time both internally and with other countries. American pride was very strong during this period of time in the early 1800s, and this impacted our economy.

The spirit of American nationalism and its economic impact in the 1800’s is often expressed in the concept of Manifest Destiny. Manifest Destiny refers to the belief that it was America’s God-given right to expand into the western areas of the continent and claim them as our own. To settle these lands despite the fact that Native Americans and Mexicans were already there required a great deal of rationalizing on America’s part, hence the need to feel that God wanted us to do it. In some cases, this philosophy resulted war.

We are all familiar with the numerous armed conflicts between the Whites and the Indians. However, our westward expansion also led to the Mexican-American War. The American victory in this war contributed greatly to America’s landholdings in the Southwest, as we picked up vast areas in Texas, New Mexico, Arizona, Nevada, and California. These states contributed to the American economy in the areas of ranching, mining, agriculture, and later, oil.

In the time just after the War of 1812, the United States experienced a rise in nationalism.  The people of the country were feeling much better about their country since they had, as they saw it, defeated Great Britain in the war.  This led them to have greater pride in the country and a greater sense of themselves as Americans.  This helped lead to a situation in which the national government tried to shape the national economy.

There are generally said to be three examples of how the government did this.  First, the government re-created the Bank of the United States.   Second, the government imposed a tariff on imported goods.  Finally, the government tried to (though it generally failed) undertake “internal improvements.”  This essentially meant the building of infrastructure such as roads and harbors.

The creation of the Second Bank of the United States, along with the tariff, helped to reshape the American economy.  Perhaps most importantly, these moves led to the creation of a diversified economy that included a great deal of manufacturing.  This started to move the American economy away from being mainly agrarian and towards becoming more industrialized.

What is an example of American Nationalism shaping national economy?

I think that one can make a case for American nationalism guiding some aspects of national economy in the 20th Century.  American nationalism and the belief of its intrinsic greatness helped to guide the national economy's interest abroad at the start of the 20th Century.  

As much of the world had accelerated the race for empire, American nationalism guided economic interests in the foreign sector.  Dollar diplomacy, the belief that American foreign interests are secured when national economic interests move into the international domain, became the simultaneous enactment of foreign policy and national economic pursuits in the Taft administration.  

The idea of dollar diplomacy was rooted in the notion the economic interests can help to smooth over potential disputes abroad.  One of the byproducts of this philosophy was to use American nationalism and its sincere belief in its own authenticity to generate foreign policy with other nations and sustain its own national economy.  Dollar diplomacy in the early part of the 20th Century demonstrates how American Nationalism shapes national economy because both Taft and Secretary of State Knox understood that foreign investment and expansion of boundaries was critical to sustain domestic economic interests.  

Dollar diplomacy does not work if there is not some level of American nationalism guiding it.  American economic interests cannot be broached with a country unless there is, on some level, an embrace of intrinsic American greatness.  It was in this where one can see American nationalism playing a distinct role in shaping the contours of national economy both domestically and internationally.