There are large rocks flying through space called asteroids. At any time, one of these asteroids could get nudged off its path just enough so that it's in earth's orbit. There are smaller rocks that fall from the sky on occasion, but a large asteroid would likely end mankind. However, this is one of the likely scenarios that could happen.
There are wars and rumors of wars. If you do some research from places like biblically.com, then you know that this is a sign of the end of the world. There are conflicts between the United States and other countries, such as North Korea, that could result in a nuclear war.
A nuclear attack would likely happen without any specific warning. A few countries have threatened this kind of attack, but there hasn't been any kind of timeline given. No country would be that brazen to announce a specific day and time. It would simply hit the button to declare war.
Perhaps one of the most realistic ways that the world might end is when a supervolcano erupts. There have been several strong earthquakes in recent years. Some have been in areas known for volcanic activity, such as Yellowstone National Park.
There are hundreds of volcanoes with activity each year, but if there are multiple explosions that are one right after the other, then it would likely send the world into a volcanic ice age.
Storms From The Sun
If you've watched weather reports, then you've probably seen details about solar flares. This is energy expelled from the sun that sometimes disrupts electronic signals on earth. A massive solar flare would likely end all communication and life because of the heat and the strength of the flare.
There isn't any clear way to determine how the world will end. The only one who knows that information is the one who created the world and who is in charge of its destination. However, there are a few clues to pay attention to that could give an indication as to the direction the world is headed.