1: Identification with one's own nation and support for its interests, especially to the exclusion or detriment of the interests of other nations.
2: The belief or desire of a government or people that a country should maintain a strong military capability and be prepared to use it aggressively to defend or promote national interests.
3: To protect themselves from other countries, mostly Germany, and prepare for attack.
4: Archduke Franz Ferdinand was a member of the imperial Hasburg dynasty in Austria-Hungary. When he and his wife were killed, Austria-Hungary declared war on Serbia which spiraled into WW1.
5: The "shot heard around the world" was the shot that assassinated Archduke Franz Ferdinand and his wife, Duchess Sophie. It basically started WW1.
6: It caused Austria-Hungary to declare war on Serbia because a group of Serbian assassins killed the Archduke and the Duchess.