The criteria for investing in diplomatic relationship shall be both the current production level of the country as well as unutilized resources like manpower and raw materials.
Though there is no limit on the money that you can invest in diplomatic relations the ideal amount will be between 5000 and 500000.
Please note that this is a sunk cost. It will only improve your relationship level with that country but will not generate any revenue. So invest judiciously.
NOTE: Please don't invest in countries which are of users with multiple user id. Those players won't be allowed in next round and hence you will lose your money for nothing.
I hope that was of some help....
Stay MastishKed...
Regards
Team HOD
