Politics of fear
“”People react to fear, not love. They don't teach that in Sunday school, but it's true.
|—Richard M. Nixon|
The politics of fear is when leaders (or candidates for leadership) use fear as a driving or motivating factor for the people, to get them to vote a particular way, allow excesses in spending, or accept policies they might otherwise abhor. It's banking on the fact that presenting people with an alleged threat to their well-being will elicit a powerful emotional response that can override reason and prevent a critical assessment of these policies.
Cheney Bush administration used this expertly since the events of September 11, 2001 to illegally invade liberate Iraq, erode civil liberties, and avoid Congressional oversight. This has been continued by the Obama administration, and doesn't seem likely to end any time soon. It is, however, not really a modern phenomenon--access to modern media simply makes it much easier to fear-monger.
 As a campaign tool
In political contests in the United States since 9/11, one or more of the candidates for election to the office in question will speak at length on the threat posed to the US by terrorism, particularly by Muslim fundamentalists, and their alleged state sponsors, so-called "rogue states". The Bush administration labeled Iraq, Iran and North Korea, amongst others, as rogue states, and suggested they formed an "axis of evil" against the US. Politicians speaking about such threats (or alleged threats) hoped that it would make voters view them as "tough" or "capable" and more likely to vote for them. This theme was extensively used in Bush's 2004 reelection campaign, epitomized by the infamous Wolves ad. The same approach was parodied in an episode of Family Guy in which Lois Griffin, a mayoral candidate, answered questions posed to her by repeatedly saying the phrase "9/11", although the questions were in no way related to the 9/11 attacks. 
 To support increased security
Similar rhetorical tools are often employed to encourage legislators or citizens to support laws that will restrict their freedom in the name of security. In the US and many of its NATO allies, government surveillance programs have been drastically expanded following the 9/11 attacks, raising concerns about infringements on civil liberties.
 In support of dictatorship
Dictators in developing nations often maintain control by inciting irrational anger in their citizens against some kind of threat (often non-existent) posed by a more powerful country (often the US) or internal opponents. Hitler famously incited fear of Jews, communists, and other "outsiders" to attain unchecked power, persecute domestic opponents and "unite" the German people into backing some atrocities.
 Culture war
“”All you have to do to secure a Republican vote is show lots of pictures of gay people kissing or black kids with their pants pulled down or Mexican babies at an emergency room. Then you push forward some dingbat like Michele Bachmann or Sarah Palin to reassure everyone that the Republican Party knows who the real Americans are. Call it the "Rove 1-2."
The politics of fear is a common tool used in the culture wars. Examples include:
- Gay rights: "gays will harm your children", and "gays who raise children are more likely to raise gays, and this is clearly bad for children". The very loaded term "defense" of marriage is at the core of the politics of fear. You need only defend against that which attacks you. "Gays who are allowed to marry will destroy the value of your marriage: Defend Marriage!"
- Less powerful, but tried nevertheless, is the use of the term "Nazi" to instill fear of feminists: "feminazis", for instance. Empowered women will take away your jobs even though they are unqualified because of some silly "equality in hiring" laws.
- Mexicans, or "illegals", are out to "take your jobs", and "destroy all you know of your land", "force you to speak Spanish", or (increasingly common) "outbreed all the whites". These examples, while not as powerful a fear tactic, still rely on loaded language to associate fearful things with whatever the target is. Similarly, African Americans use affirmative action to take your jobs – and even get their ideas into politics, de-fanging the police. Oh noes!