International politics concerns the interactions among different nations, including their power struggle to influence each other. This is at the local, regional, national and global level and includes governments, regional blocs such as the EU, multinational corporations, political movements like NGOs and the security forces.
Usually, the primary interest of any state is self-preservation but can also include economic prosperity and the ability to control foreign entities. In the case of diametrically opposed interests, states must either negotiate or fight. For example, a US administration may disagree with its European and Asian allies over trade policy but is unlikely to go to war because doing so would harm the country’s own economy. This is a good example of complex interdependence in the modern world.
Realism, on the other hand, views the world as a dangerous place full of hostile states that are constantly competing for resources and control over weaker ones. This competition is driven by the need to project military and economic power over other states, which is why most countries pursue a balance of powers strategy.
Alternatively, liberalism offers a more positive view of the world, which is that states can cooperate in their mutual pursuit of peace and prosperity. However, it is not because they are morally driven, but rather because institutions create the norms and rules that make cooperation possible. For example, a democratic peace theory suggests that democracies only go to war with each other for legitimate reasons and are more willing to share their wealth than non-democratic states.