Answer:
In the 1600's and 1700's the original 13 colonies of the USA began as British colonies. While there was other land in North America outside of the colonies, some was under French rule... and much of it was relatively unsettled and unexplored by the Europeans.
Over time, there were eventual complaints of taxes being sent to Europe, and no local control over the ruling European Government policies. Perhaps communication issues would have limited true representation anyway.
In 1775 a Revolution was started by the Americans vs. the British. In 1776 a Declaration of Independence was signed and the war ended in 1783 becoming the the nation we are today.
Even though many of the European governments were monarchies, most of them had some kind of courts, and a multi-tiered government. While a monarchy, England even had a parliamentary system since 1707. The American Founding Fathers would also have been aware of previous democratic systems in Greece and Rome as well as contemporary European systems from which they could derive ideas.
Initially there was a deep concern for local and state rights vs national rights. The first US Government was under the Articles of the Confederation, first drafted in 1777, and ratified in 1781.
Difficulties eventually arose requiring a better defined central power.
A constitutional convention was called for in 1786, and the constitutional convention took place in 1787. The constitution was ratified in 1789.
Initially there were not general elections, but rather the president was determined by an electoral college, vestiges of which remain today.
The first president, George Washington was immensely popular, and was the only president ever elected unanimously. With this popularity, he had an opportunity to shape the country. His deep conviction to democracy lead to a convention of limiting presidential terms in office to 2 terms or 8 years which held until Franklin Roosevelt (now the 22nd amendment).
The initial United States only covered 13 states, and it eventually expanded from the Atlantic to the Pacific through colonization, land purchases, and various wars and battles. Building a national infrastructure including the building of railroads was also in the expansion of the country.