Difference between 'relation' and 'relationship'?

[Rebecca]

Hi,
Please have a look at this sentence:
"In order to understand what people are saying, you need to take into account the RELATIONSHIP between speakers and their situation"
Could anyone tell me why we use 'relationship', not 'relation'?
By the way, what is the difference between these two words?

Thanks in advance! :P

[Inga]

relation between people is usually used in plural: Relations between the two countries have improved recently.
or the special relationship between Britain and the US
In the meaning of 'the way in which two or more things are connected and affect each other' relationship between can be used: the relationship between poor housing and health problems, or A related classification of political systems also emphasizes aspects of the relationship between the rulers and the ruled.
(I used Longman dictionary for examples.)
_________________
I am an incurable optimist.

[Rebecca]

Thank you very much!