Why does the US have a 2-Party System? What institutional factors support a 2 Party system and prevent 3rd parties?

he two-party system came into being because the structure of U.S. elections, with one seat tied to a geographic district, tends to lead to dominance by two major political parties

Explanation:Even when there are other options on the ballot, most voters understand that minor parties have no real chance of winning even a single office. Hence, they vote for candidates of the two major parties in order to support a potential winner. Of the 535 members of the House and Senate, only a handful identify as something other than Republican or Democrat. Third parties have fared no better in presidential elections. No third-party candidate has ever won the presidency. Some historians or political scientists might consider Abraham Lincoln to have been such a candidate, but in 1860, the Republicans were a major party that had subsumed members of earlier parties, such as the Whig Party, and they were the only major party other than the Democratic Party.

just like you man, i personally think its either c or d

explanation:

but good luck with the test man

answer:   migrations were important in the neolithic period. "two major migrations passing through southeastern europe were confirmed by the means of archaeo-genetic studies."

the first migration was the early neolithic period -- 6,000 before common era (bce) -- when the first farmers, from anatolia -- asia minor -- spread through europe. the second migration occurred during the early bronze age (3,000-2,500 bce) when the so-called "steppe population," from the eurasian steppe, replaced much of northern europe's previous population.

the first farmers of northern and western europe passed through southeastern europe with limited hunter-gatherer genetic admixture, which occurs when two or more previously isolated populations begin interbreeding. however, some groups that remained mixed extensively -- without the male-biased, hunter-gatherer admixture that prevailed later in the north and west, according to latest discoveries. southeastern europe continued to be a nexus between east and west, with intermittent genetic contact with the steppe people up to 2,000 years before the migrations that replaced much of northern europe's population.

"in some places, hunter-gatherers and incoming farmers seem to have mixed very quickly," says iain mathieson, a geneticist at the university of pennsylvania, who was first author of the paper. "but, mostly, the two groups remained isolated, at least for the first few hundred years. these hunter-gatherers had been living there for thousands of years, and it must have been quite a shock to have these new people show up -- with a completely different lifestyle and appearance."