The main carriers of nationalism during colonial period were the urban middle classes. Here's why:

1. Education and Exposure
- The urban middle classes had access to education and exposure to Western ideas, which contributed to their awareness of the social and political conditions of their country under colonial rule.
- They were also exposed to the ideas of liberal nationalism, which emphasized the importance of individual rights, representative government, and the rule of law.

2. Economic Interests
- The urban middle class had economic interests that were affected by colonial policies. For example, they were affected by discriminatory trade policies that favored British goods and limited the growth of local industries.
- They also faced competition from British merchants and traders who dominated the economy.

3. Political Participation
- The urban middle class had opportunities to participate in the colonial administration and politics. They were often appointed to positions in the colonial bureaucracy and were involved in local government.
- Through their participation in the colonial administration, they became aware of the limitations of the colonial system and the need for political reform.

4. Press and Literature
- The urban middle class had access to the press and literature, which allowed them to express their opinions and spread their ideas.
- They used newspapers, books, and pamphlets to criticize colonial policies and to promote their vision of a free and independent India.

In summary, the urban middle class was the main carrier of nationalism during the colonial period because of their education and exposure, economic interests, political participation, and access to the press and literature. They played a key role in the Indian nationalist movement and provided the leadership and intellectual framework for India's struggle for independence.