why do political parties involve partisanship
The following points may help you:
a. Parties divide the society on the basis of ideologies that its supports and endorses.
b. Parties involve partisanship where people show affiliation to a particular party and its ideology.A person strongly committed to a particular party and its ideologies, it means a strong sense of affiliation towards a particular party or a group and favoring its policies and programmes over others.
c. A party seeks to promote and upholds a particular interest. For example regional parties, caste based parties.
d. A party comprises of a leader who is actively propagating his/her party's programme and beliefs, active members who are associated with it and followers who believe in its programmes.
e. Parties tend to divide people for instance , caste based parties creates division in terms of pro reservation and anti reservation group.
f. Then there are regional based parties which may at times demand greater autonomy or even secessionism from the Union,