Direct standardization is used to compare the mortality rates between two countries. This is done because of the difference in-
Adjusted or standardized rates

Standardization (or adjustment) of rates is used to unable the valid comparison of groups that differ regarding an important health determinant (most commonly age).
For example, if we want to compare the death rates of two different populations with different age composition, the crude death rate is not right yardstick because rates are only comparable if the populations upon which they are based are comparable.
To remove this confounding effect of different age structure, adjustment or standardization is done.
Two major approaches to standardization have been used :-


Direct standardization
Indirect standardization
Causes of death
Numerators
Age distributions
Denominators