What were the causes and effects of the War of 1812?

The short answer is that the primary cause of the War of 1812 was the British putting in place extraordinary maritime measures to prevent the American business interests from trading with other European countries, specifically France. The Americans saw the expansion of trade critical to the economic success of the country. The British were engaged in a long-term war with France, which began around 1795. The French countered the moves by the British and attempted to limit American trade with the British. America was caught between two foreign powers both, which they desired to keep friendly economic relations. What was primarily a European dispute erupted into a war jeopardizing American interests overseas and in mostly French-held lands west of the Mississippi River.
Both the French and British attempted to solicit help from Native Americans, who were suspicious of western expansion from territories east of the Ohio River Valley and Mississippi River. Eventually, the bulk of Native American tribes either sided with the French or moved further west, attempting to remain neutral. In November of 1811, after years of trying to find a negotiated settlement with Great Britain and France, President Madison called a special session of Congress.
In a close split vote in the House and Senate, in June of 1812, a declaration of war was introduced and passed. The vote split the Northern from the Southern Congressman and Senators, as the north (where the important ports were located) favored negotiated settlement with the British and a return to expanding trade. The south and west were in favor of going to war, as their interests were far more local than international.
Some historians claim the desire to fight Great Britain by southern and westerners was a belief that the British maritime infractions were an insult to the international reputation of America, and war was the only recourse to restore America in the eyes of the international community. At any rate, historians generally agree the British were caught off-guard by the declaration of war and were much concerned they would be fighting a war on two continents.
The immediate effect of the War of 1812 was economic. The entire American continent suffered from not being able to trade internationally. Some economists believe the war led to the earliest recorded depression in United States history, which Jefferson warned the nation about in 1814 and officially started in 1819.
The War of 1812 hurt the fledging economy of Great Britain as well. Over-expansion into colonies and rising costs of the war crushed British economic fortunes. The result was that over time, the British were unable to sustain their position as the economic leader in the world and premier naval power. The decline of British power was remarkably swift in the eyes of some historians.
The United States had purchased from the French the lands west of the Mississippi River in 1803, doubling the size of the United States territory. Until the War of 1812 ended, settling and controlling the area was made difficult by French and British fighting—additionally, both nations incited Native Americans to fight settlers moving west. The most detrimental effect of the War of 1812 is the exacerbation of American regional hostilities between northern and southern interests. The close votes in Congress and the subsequent political arguments were the first signs of a potential threat to a unified federal system of states.
Eventually, these arguments were the precursors to the battles over slavery and, in the end, civil war. Finally, the United States established itself as a potential filler to the vacuum of power left by European interests embroiled in political battles on European soil and beset by severe economic problems that restricted their ability to expand. The United States was no longer hindered to grow west on the American continent and had proved itself internationally as a military power capable of defending its interests abroad.
https://history.state.gov/milestones/1801-1829/war-of-1812

https://www.fpri.org/article/2017/03/causes-war-1812/

https://www.theglobalist.com/panic-of-1819-the-first-major-u-s-depression/