Every democratic country, and some autocracies, have political parties. A political party is an organization that exists to recruit and promote candidates for public office that support some political agenda. Parties make office holders, and parties are the primary means of advancing a political agenda. The number and nature of political parties in democracy is a function of the state's electoral laws. The reason Israel has a multitude of small religious parties is because the electoral laws are written to encourage such small parties. The reason the United States has two large parties and all other parties are largely irrelevant is also a product of American electoral laws. This writeup will show why that is so.
In writing this we assume a democracy, which means the elections are free and fair. It also assumes that the political system has been stable long enough for the party system to shake out a bit.
The United States is the foremost example of a pure ‘winner takes all, first past the post” electoral system. In the US, the candidate who gets the most votes wins. Nobody else gets anything. So if fifty-five candidates run for president, and each gets two votes, except for one guy who gets three, the guy who gets three votes gets the job. Everyone else goes home.
This means that only three voters were really happy with the election outcome. Everyone else is dissatisfied, particularly those who are more ideologically opposed to our three vote winner. Some of them will unite for the next election, and the group that puts together the largest coalition will win. Simple evolution will assure that in the end you will end up with two large political parties, because that's the only way to have an outcome capable of achieving partial success.
Note the term partial success. The kind of party that emerges is large party, ideologically heterogenous, that is essentially a large coalition of people who share more with each other than the other large party. They are what you call 'Big Tent' parties. It is very rare that such parties nominate candidates who agree with everything you do, but they do produce candidates who differ in meaningful ways from the other party. Voters then vote for the candidate whose policy 'mix’' best resembles what they approve.
This sort of candidate produces frustration. Voters often don't get to choose someone they really want, which means they often end up voting 'against' the other guy. The key problem for candidates is holding their coalition together while appealing to the undecided voters. This forces candidates toward the political center during the general election. That often angers their supporters whose beliefs are more ideological.
The problem is that leaving the coalition is usually suicidal for the ideological extremists. Pat Buchannan's run for president in 1992 is often considered a factor that contributed to the victory of his ideological opponent, Bill Clinton. Ralph Nader's run in 2000 possibly cost Al Gore two states in that election, handing the presidency to Nader’s ideological opponent, George W. Bush. Both Buchannan and Nader represent the far edge of mainsteam politics in the United States. While their supporters appreciate their candor and ideological purity, much of what they say is frightening to the center. Extremists are seen as ‘unelectable' by others who share much of their views, but whose primary interest is getting the best possible person into office. Most go for the best deal possible.
Supporters of Nader and Buchannan get nothing for their efforts, except the election of the person they really did not want. If they raise an issue that captures the political mainstream, one or both of the two mass parties will shift to capture that issue.
This explains why the Democratic and Republican parties are the only parties that really matter in the US electoral system. America has a multitude of political parties, all small, ideologically pure and irrelevant. A third party may capture local office in a specific geographic region. But nowhere else.
For a third party, say the Green Party, to become a national factor they must replace one of the two mainstream parties. Consider this scenario: For years religious conservatives have grown increasingly powerful inside the Republican party. In many cases they have taken control of the nomination process. But while America is a religious country, it is not fundamentalist. Essentially Ralph Reed, Pat Robertson and Jerry Falwell have shifted the Republicans to the far right. Eventually the conservative "purity quest" will produce a counter-reaction leading to widespread defeat of GOP candidates,
This will produce a lot of soul-searching among Republicans. Theory predicts they will attempt to move left to recapture the political center they have abandoned. That shift may not take place if religious conservatives interested in ideological purity retain sufficient control of the party. They may wish to shift further to the right, arguing their problem was insufficient purity.
If the conservatives win theory predicts disaster for the Republican Party. The righward shift will alienate even more mainstream voters. Republicans will lose a lot of elections, and either fold, become a Bible Belt regional party, or abandon Cal Thomas and shift left. If they do not shift back to recapture the center the Democratic Party will move to the right and happily occupy the political center, and for a time win a lot of elections. But their move right will anger the Democratic left who will abandon their party for the Greens. Many of these Democrats will bring a pragmatic point of view with them, shifting the Green party to the right, occupying the space abandoned by Democrats.
This is what must happen for the Green party to win office at the state or national level. They must become the Democrats by another name, and the Democrats will become like the Eastern Republicans of the 70's. The theocratic remains of the Republican party will become regional or irrelevant. America will end up where it started with two mass political parties, one slightly left of center, one slightly to the right. The names will have changed, but nothing else.
Israel is an extreme example of the proportional representation system of government. Under proportional representation political power is shared in rough accordance with the total number of votes, Under proportional representation you vote for party lists, and the number of candidates your party lands in power depends on how many people voted with you. Nobody 'wastes' their vote
This system offers some pluses. The multiplicity of parties means most people get to vote for someone with whom they agree with on almost everything. This produces a real sense of involvement. There is a party for you. Candidates can speak more freely without fear of being punished by the electorate.
The problem comes after the election, when the 'winner’ must form a government. Since no party has a clear majority coalitions must be assembled from the multiplicity of smaller parties. Someone must put together a majority of allied parties from the fragmented many. This produces some fairly odd political bedfellows with some strange policy outcomes.
For example, in Israel orthodox rabbinical students are exempted from military service. Only orthodox conversions are recognized as valid for immigrants. These outcomes are largely unpopular in Israel, but were pressed through because a few small ultra-orthodox parties were needed to form a coalition. Those laws were the price of Ultra-orthodox participation in government.
Such coalitions also have an extraordinarily hard time facing difficult issues. Smaller coalition parties can threaten to leave at any time if they don't get their way, bringing down the government and forcing new elections. This limitation paralyzed the government of Weimar Germany, helping lead to hyperinflation and Hitler. It means that when you need a majority on a really critical issue, you may not be able to get it.
Political scientists talk about two processes occurring around an election. The first is interest articulation, which is simply people saying what they think ought to happen. The second is interest aggregation, where policy makers sort through the articulated interests and put together a "cocktail" of policy goals to be pursued.
Under the American ‘'winner take all’' system with the big mass parties this process generally takes place before the election. The policy mix which emerges—which used to be a party platform— is visible before the election, and retains some ideological coherence. You may not get to vote for the candidate you really want, but you do get to vote for something of the government you really want.
Under proportional representation this process takes place after the election, so secular peace activists and reformers may form alliance with political conservatives. You get to vote for the good guys, but you don't know who their partners will be until after the new government is assembled. Your vote may help someone you really dislike take power.
Proportional representation also generates anti-system parties whose policy goals may be antithical to the system itself. If you get to vote for your favorite candidate, so does the Hitler Youth. Generally the more mainstream parties will form coalitions to keep perceived anti-system parties out of power, so a vote for them also ends up wasted. An example of this came in post World War Ii Italy, where for years Italian parties did everything possible to keep the Italian Communist party out of government.
There are many variations and modifications of the above system. Unwilling to countenance the paralysis of the Weimar Republic, post war Germany adopted proportional representation with a 5% floor. To take even one seat in the Bundestag a political party must get at least 5% of the popular vote.
That gets rid of real fringe parties, and leaves Germany with a three or four parties, with one party—until recently the Free Democratic Party—as coalition partner with either the Socialist or Christian Democrats. German parties tend to be more ideologically coherent than in America, but nowhere nearly so as in Israel. In France they require that a winner get over fifty percent of the votes. This leads to coalition formations before the elections, as both sides work to win the runoff election. For example, when Francois Mitterand was first elected President of France, he invited the French Communist party into coalition with him. They could not refuse, and after the election found themselves dealing with a labor crisis, in opposition to their main supporters, French unions. In 2002 neo-nazi Jean Marie Le Pen finished second in the national election, forcing the French left into coalition with the conservatives in order to keep the National Front from office.
Party structures are not the product of illuminati conspiracies or the Trilateral Commision. They are simply a function of a state's election laws. America has the muddy Republicans and mixed Democrats because the laws dictate it. Israel's Ehud Barak took the ultra-orthodox Chac party into government because Israel's constitution was written to mandate everyone be heard. In the United States if Ralph Nader's Green Party wants to win a general election, the price will be the very ideological purity their supporters like. They must become Democrats, which means Mr. Nader could never become their nominee.