Many of the questions can be answered simply by browsing Wikipedia.
http://en.wikipedia.org/wiki/Silk_roadSimple geography (and/or 'hostiles' to the north):
http://en.wikipedia.org/wiki/Triangular_tradeThe particular routes were historically also shaped by the powerful influence of winds and currents during the age of sail. For example, from the main trading nations of Western Europe it was much easier to sail westwards after first going south of 30 N latitude and reaching the so-called "trade winds"; thus arriving in the Caribbean rather than going straight west to the North American mainland. Returning from North America, it is easiest to follow the Gulf Stream in a northeasterly direction using the westerlies. A similar triangle to this, called the volta do mar was already being used by the Portuguese, before Columbus' voyage, to sail to the Canary Islands and the Azores. Columbus simply expanded the triangle outwards, and his route became the main way for Europeans to reach, and return from, the Americas.
http://en.wikipedia.org/wiki/Christopher_ColumbusIn the context of emerging western imperialism and economic competition between European kingdoms seeking wealth through the establishment of trade routes and colonies, Columbus' speculative proposal, to reach the East Indies by sailing westward, eventually received the support of the Spanish crown, which saw in it a chance to gain the upper hand over rival powers in the contest for the lucrative spice trade with Asia. During his first voyage in 1492, instead of reaching Japan as he had intended, Columbus landed in the Bahamas archipelago, at a locale he named San Salvador. Over the course of three more voyages, Columbus visited the Greater and Lesser Antilles, as well as the Caribbean coast of Venezuela and Central America, claiming them for the Spanish Empire.
Though Columbus was not the first European explorer to reach the Americas (having been preceded by the Norse expedition led by Leif Ericson in the 11th century[7]), Columbus' voyages led to the first lasting European contact with the Americas, inaugurating a period of European exploration, conquest, and colonization that lasted for several centuries. They had, therefore, an enormous impact in the historical development of the modern Western world. Columbus himself saw his accomplishments primarily in the light of spreading the Christian religion.[3]
Never admitting that he had reached a continent previously unknown to Europeans, rather than the East Indies he had set out for, Columbus called the inhabitants of the lands he visited indios (Spanish for "Indians").[8][9][10] Columbus' strained relationship with the Spanish crown and its appointed colonial administrators in America led to his arrest and dismissal as governor of the settlements on the island of Hispaniola in 1500, and later to protracted litigation over the benefits which Columbus and his heirs claimed were owed to them by the crown.
On colonialism and the benefits of guns and steel:
From the 12 October 1492 entry in his journal, in which he wrote of them, "Many of the men I have seen have scars on their bodies, and when I made signs to them to find out how this happened, they indicated that people from other nearby islands come to San Salvador to capture them; they defend themselves the best they can. I believe that people from the mainland come here to take them as slaves. They ought to make good and skilled servants, for they repeat very quickly whatever we say to them. I think they can very easily be made Christians, for they seem to have no religion. If it pleases our Lord, I will take six of them to Your Highnesses when I depart, in order that they may learn our language."[49]
Columbus remarked that their lack of modern weaponry and metal-forged swords or pikes was a tactical vulnerability, writing, "I could conquer the whole of them with 50 men, and govern them as I pleased."[50]
...
The scholar Amerigo Vespucci, who sailed to America in the years following Columbus' first voyage, was the first to speculate that the land was not part of Asia but in fact constituted some wholly new continent previously unknown to Eurasians. His travel journals, published 1502–4, convinced German cartographer Martin Waldseemüller to reach the same conclusion, and in 1507—a year after Columbus' death—Waldseemüller published a world map calling the new continent America from Vespucci's Latinized name "Americus". According to Paul Lunde, "The preoccupation of European courts with the rise of the Ottoman Turks in the East partly explains their relative lack of interest in Columbus' discoveries in the West."[100]
etc, etc.