At the beginning of the game, staking out as large a territory as possible is desirable to many people. If you manage to start with a scout and find land bridge of one to two squares between certain areas CLAIM it!.
Very early in the game you can fortify your warrior or scout at this location and nothing can pass through. This effectively denies any civ from getting through to find building sites, other civs to communicate with and villages to plunder. You then become the gate keeper of whether to allow the civ communication with the other one or not.
a one land square bridge is a no brainer to block…
LLLLLL
xLLLxx
xxbxxx
xLLLx
LLLLLL
where L is land and x is water and b is the one square. Simply fortify your unit there and when you get a settler put it at that location. ANOTHER BENEFIT to this is that you now have essentially a canal through the continent, saving on distance when the game turns to naval operations.
a look at the more common 2-3 land square bridge
LLLLLL
xLLLLx
xxLLLx
xxbdxx
xLLLxx
LLLLLx
LLLLLL
This is still easily solved by placing a city b and fortifying a unit at d.
you can do this with a size 3 land bridge but you must be quick because to assemble a city and get 2 units fortified before the other civs come through takes some doing.
BEWARE, the AI knows the value of single square land bridges. While playing Marla Singers world map, the computer fortified a spearman at one of the single square land bridge spots between north and South America.
If the choice is to continue through the choke point and discover another civ while an enemy civ’s scout is on your tail to follow through, it is better to just park it there and deny them that chance. You then become the gate keeper and determine when to let them have communication and sell tech to them.