The answer is b) It created resentment and often hindered negotiations in Europe.
Let's look into it one by one:
a) It established unity and peace among European countries. -This is not true.
-Nationalism has caused the civilian of nations to want to protect themselves as well as get national glory by getting land. This caused territorial conflict and hostility between each nations instead of peace and unity.
b) It created resentment and often hindered negotiations in Europe. - This is correct.
-As mentioned, nationalism has caused conflicts of territorial interest between nations. The nations were wary against one another that they might be attacked. They are also unwilling to back down in order to get national glory and show their superiority of the nation. This had indeed caused resentment and many negotiations went unsuccessful such as the disarmament conference.
c)The feelings of nationalism created a wave a optimism about peace in Europe. - This is incorrect.
- The feeling of nationalism had caused the up rise of aggression which made the nations to be suspicious towards one another causing negative impact about peace in Europe.
d) Nationalism had no impact on Europe during the late 19th and early 20th centuries.-This is false.
-As the above mentioned, nationalism had significant impact on the development in Europe.
Therefore the answer is b) It created resentment and often hindered negotiations in Europe.
Hope it helps!
