Despite what is depicted in shows like Star Trek, advanced life is probably rare in our galaxy for many reasons. Whether it’s due to natural phenomena, on the planet or from even outside a star system, to events caused by the civilizations themselves. The Drake Equation postulated by Frank Drake in 1961 doesn’t take all these different events into account and oversimplifies the number of advanced civilizations in the galaxy.
Phenomena on the planet that could limit civilizations range from volcanoes to disease. Volcanoes, if they have large enough eruptions could blanket the planet in volcanic ash blocking out the planet’s star, causing a volcanic winter resulting in the death of millions of species.
Extreme temperatures can hinder civilization development. Greenhouses becoming trapped is another factor. Temperatures become too hot, drying up oceans. It could also result in the atmosphere becoming thicker and crushing anything on the surface like on Venus. Global ices ages can also kill off surface life. Ocean life would fare better, with heat from hydrothermal vents.
The disappearing of a planet’s magnetosphere would also lead to severe consequences to any life on a planet (unless they were intelligent enough to go below ground.) Without a magnetosphere a planet has no way of protecting life from a star’s cosmic radiation. This is believed to have happened on Mars after is core stopped spinning.
Finally you have disease. Until a civilization is advanced enough to deal with disease, it can be very crippling to a struggling society. This is one of the contributing factors to the Dark Ages (some of the others will be discussed later.)
Moving on to phenomena within a star system. Most common are asteroids and comets, which are believed to have cause the extinction of the dinosaurs. These would have similar effects to volcanoes, in that they would block out the planet’s star. If a fledgling civilization (like ours) isn’t properly prepared they could meet the same fate as the dinosaurs.
The star itself can be a danger to life. Depending on it’s type or age it could either become a red giant (like our is destined to do) or go supernova. A red giant would cause the atmosphere and oceans to burn off and possibly even encompass the world. A supernova would annihilate a planet completely.
Stars outside the planets star system can also affect life. A strong enough black hole near a star would eventually cause that system’s demise. A rogue star ( a rarity) could shift a planets orbit and disrupt life.
The most frightening (because it’s not entirely predictable) is the Gamma Ray Burst. If a star is close enough it could wipe out life in another system with a Gamma Ray Burst. It would wipe out a planet’s ozone layer and cause an Extinction Level Event.
As much as we like the think alien civilizations are more advanced then us, they most likely will have the same problems as us. Unlike on Star Trek, planet’s will most likely have several religions, races, styles of government, which will lead to some of the conflicts described below.
Majority of species on Earth are territorial, this most likely be true on other worlds as well. Civilizations have been fighting over territory for thousands of years. (Russia trying to take back Ukraine is a recent example.) They are willing to take it by force and murder (i.e. War which I will discuss later).
Race is another major divisive factor. Look at what it has led to here on Earth. Slavery, lynches mobs, Nazi’s, KKK, etc. This will likely occur on other planet’s too. Especially ones like Earth that has varying environments and life adapting to those different environments.
Tribalism is also a cause of strife between similar peoples. People hating each other just because they are from a different family, clan, tribe, etc. Most recent examples are the ethnic cleansing in some African countries.
Differing governing styles can also lead to conflicts in a civilization. Whether it be extreme right wing fascism or extreme left wing communism, or from a monarchy to a democratic republic. Some changes can be peaceful or very violent leading from hostile takeovers to civil war.
Religion is the most divisive of all. Leading to wars, the Dark Ages, oppression etc. Even divisions within religions. Most recent being Catholics vs Protestants in Northern Ireland. People were wary of a Catholic being in office when JFK ran, or how Muslims are treated in modern society.
Religion can also lead to lack of scientific advancement. Religions have often suppressed science that opposed their ideology. Alien Civilizations will more than like have hundreds of religions of their own.
These factors and the fighting over resources, such as oil, will lead to war. Some can be short skirmishes some can last for years, killing millions. And can also lead to nuclear annihilation. Other civilizations might not be as lucky as us, and have already wiped each other out.
Civilizations could also hinder themselves by destroying their environment. Speeding up natural climate change, destroying their ozone layer, pumping toxins in the atmosphere that can’t be naturally dealt with and build up and wreak havoc on the environment.
The last factor wouldn’t necessarily destroy a civilization (unless it lead to a deadly civil war) but could hinder the advancement of civilization in general. If an empire (best example the Roman or British Empire) over extends itself without having the resources to properly govern and control it, could lead to its collapse and take time for some to recover to build their own countries or empires. It make take time for a civilization to stabilize from such events.
More than likely other worlds would go through several of these and not just one. Say for example a world’s scientific development was hinder by religion and they weren’t advanced enough to deal with an asteroid, they could be wiped out. Or two countries go to war over a fight for territory and use nuclear bombs, they could wipe each other out and maybe even cause a global catastrophe. Combination of these factors would severely limit the number of advanced civilizations in the galaxy and the Universe as a whole.
For information about the Drake Equation : http://www.seti.org/drakeequation