Final answer:
The high turnout in the 2008 Democratic Party precinct conventions was chiefly due to the historic nature of the primary election candidates and pressing national concerns like the Iraq War and financial crisis, as well as changes to the delegate selection process.
Step-by-step explanation:
The chief cause of the incredibly high turnout in the 2008 precinct conventions for the Democratic Party was the combination of a historic and tightly contested primary election along with national concerns that spurred voter engagement. In the 2008 Election, there was the possibility of New York Senator Hillary Clinton becoming the first female nominee by a major political party, while ultimately, the first-term senator from Illinois, Barack Obama, secured the nomination, becoming the first African American nominee. The excitement around these historic firsts, combined with the general dissatisfaction with the ongoing Iraq War and the dramatic financial crisis, significantly influenced voter turnout. Moreover, the changes in how delegates were chosen following the chaos of the 1968 convention, which aimed to reduce the sway of party elites over the nomination process and give more voice to primary voters, likely contributed to increased participation in the Democratic caucuses and primaries.