creation expansion and interaction of political systems
The passage of the Indian Citizenship Act in 1924 granted citizenship to all Natives born in America. As a result, Native Americans were finally granted free travel in the United States. At the present time, Native Americans who live on reservations are free to travel as they wish.
And 1540s, the Spanish Crown divided the American empire into two immense regions, known as viceroyalties, each ruled by a viceroy appointed by the king. The viceroyalty of New Spain consisted of Mexico, Central America, and the Caribbean islands.
Cyanobacteria, also known as "blue-green algae", are the unicellular organisms which are able to produce oxygen.
Approximately 540 years ago, the atmosphere was very poor on oxygen. Cyanobacteria are thought to be responsible for the oxidization of the atmosphere back then, in an event known as <em>"The Great Oxygenation Event"</em>. As a result, Earth's life forms suffered drastic changes in their composition, as they evolved from being <em>anaerobic</em> to becoming organisms <em>highly dependant</em> on oxygen. The oxygenation of the atmosphere would eventually provide the adequate environment in order for the <em>Cambrian Explosion</em>, or the first diversification of living organisms, to happen.