What determines whether or not a particular country embarks on the road towards democracy, whether it completes that voyage successfully, and whether ot eventually consolidates democratic vaules, pratices, and institutions?
There are a number of variables that determine whether a particular country adopts a democratic government or even goes down the path towards a democracy. A lot of it has to do with the political history of the county and its people. Satisfaction also plays an important role, as does culture.
A democracy is based on the general idea that the people within the community are the best ones to decide how the community is governed. The people appoint, and remove, the leadership, according to how well the leadership tends to the needs and desires of the community.
A community that has a strong tradition and history of being successfully governed by non-democratic governments are less likely to be inclined towards seeking a democracy, because they are successfully governed using a different method. Why change it if it works?
The most common reason for countries to try to adopt a democratic government is because the previous government method has been overly concerned with meeting the desires of the people within the country. An example would be a king who excessively taxes the population into starvation in order to fund a lavish lifestyle for the royal court.
Some states do not complete this 'voyage' to democracy because the people find a happy medium between authoritarian and democratic government that suits them better. The UK is one example of this, where there is both a monarch and an elected element to the government. Other states do not successfully establish a democracy because there is a very fine line between a true democracy and an oppression of the minority (or majority) by the majority (or minority) who have taken control of the government and ensured that they will be able to implement their desires regardless of that of the collective community.