• [The July Crisis] (http://www.reddit.com/r/AskHistorians/comments/32oepq/why_did_the_german_forces_go_around_paris/cqdfutv?context=3)
• [Lead up to and outbreak of WWI] (http://www.reddit.com/r/AskHistorians/comments/35vtov/discuss_the_causes_of_world_war_i_what_were_the/)
• [Balkan Nationalism and the Outbreak of WWI] (http://www.reddit.com/r/AskHistorians/comments/37n91p/to_what_extent_did_ethnic_and_nationalist/)
• [To what extent was WWI inevitable?] (https://www.reddit.com/r/AskHistorians/comments/3faq1j/i_have_always_heard_war_was_inevitable_prior_to/)
• [Could the July Crisis have been resolved peacefully?] (https://www.reddit.com/r/AskHistorians/comments/3vq7mq/how_many_attempts_were_there_to_stop_the_first/)

but which State had the most to do with these factors, to the point that blame could be placed on them?

I wouldn't say one state with regards to the lead up to war, as "unilateral war guilt" was never asserted nor was it the issue with the Versailles Treaty, as I've elucidated in numerous answers. With regards to the July Crisis, Germany's actions, especially the Blank Check and the declarations of war on Russia and France lead to the outbreak of WWI.

Tough one.

Can we say Austria-Hungary? By invading Bosnia & Herzegovina and because the July Ultimatum followed by the declaration of war to Serbia?

Just asking historians.

This is an extremely difficult question, but the blame could realistically be put on Austria-Hungary for declaring war on Serbia before investigating whether Ferdinand's assassin was affiliated with the Serbian government, or one Germany for encouraging and facilitating the invasion of Serbia.