SEATTLE — Amazon, the colossus of internet commerce that was founded here, is conducting the most dramatic sweepstakes of modern capitalism in throwing open a competition for a coequal second headquarters. The company has promised to create about 50,000 new jobs at HQ2, as Amazon is calling it, paralleling the similar number the company plans to employ here over the next couple of years.

Six-figure salaries, real-estate investments and economic ripple effects — from health care for all those new workers to the hash browns being served for breakfast — could inject $50 billion or more into the winning town, economists say. Proposals from 43 states, the District of Columbia and Puerto Rico, as well as Canada and Mexico, are now being considered, with a decision scheduled for sometime next year.

For Seattle, Amazon has become far more than a big employer and taxpayer. It reshaped how the city sees itself and, in turn, is seen by the world. It created a vast, gleaming new campus in a once derelict corner of the city, but also raised deep concerns about housing costs, traffic congestion and potential over-dependence on one corporation.

In interviews with experts and residents, from tech company offices to chambers of commerce, here are the lessons from Seattle for all those cities now seeking the Amazon prize.