You have a foreign constraint on your tig_pairs table referencing the tig_nodes table. However, you are not inserting any data into tis nid field. The referenced field tig_nodes.
Nid doesn't allow NULL values. Due to these two constraints, you cannot INSERT null into the nid field of tig_pairs .
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.