The owner of a territory that has access to numerous continents can exercise a great deal of power over others. Likewise, he will also be subject to attacks from others as they may need to get through him to get to their goal. Hence, attempt to be the first person to conquer such territories to maximise your political gain and lead the strategic attacks.
There are a number of choke points, or so called intersection grounds in the game that are absolutely critical to control. Owning them gives you more options when you want to attempt surprise attacks or respond quickly to enemy army rearrangements. A classic example is Middle East. This territory has access to three continents and a large army in this strategic location can threaten players in Asia, Europe, Africa and even Australia. There are of course other intersection grounds.
Please vote on where you think these intersection grounds are.