"to that end" = "to achieve that purpose" example: "John decided to bake cookies. To that end, he started to collect the ingredients: flour, chocolate, and butter."

'To that end', in this context, indicates that the methods or functions set out in the text after 'to that end' are those which help to achieve the goals set out in the text before 'to that end' - in this case, 'international peace and security'. I would imagine the methods or functions set out after 'to that end' included things like 'diplomacy', 'arbitration', 'accords', 'treaties', and 'regulations', all of which are there to achieve 'international peace and security'.