Final answer:
The disappearance of the single issue party can be attributed to the difficulty of maintaining party autonomy within the two-party system and limited support among the electorate. However, these parties have also brought important issues to the attention of the major parties.
Step-by-step explanation:
The reason behind the disappearance of the single issue party can be attributed to several factors. One of the main factors is that single issue parties often struggle to maintain party autonomy and distinct party identity within the growing two-party American political system. This is because they align themselves with one major party that shares similar ideas, and when they lose, their party structures collapse.
Another reason is that single issue parties typically champion narrow sets of causes, leading to limited support among the electorate. Once their leaders are defeated or discredited, the party structures built around these leaders collapse, and supporters often return to the major parties.
However, single issue parties have also played a role in bringing important issues to the attention of the major parties, who have incorporated these issues into their platforms over time.