When a string is loaded within its elastic limits, then the strain increases rapidly.  Hence, stress increases. At a particular point called the breaking stress, the string breaks. The force responsible for this is called breaking force

Breaking force depends on the area of cross-section of the wire. This is not dependent on the length of the string or its thickness and it is a constant for the given material.

Hence, when the string is cut into two or more parts, the breaking force would be the same and is also independent of the length factor. So the maximum load which the string can withstand will be the same, even when the string length is reduced to half.