Birth-based caste system has no sanction in the Vedas or vedic religion which proclaims the equality and brotherhood of all human beings. It similarly has no sanction in Sikhism, Buddhism and Jainism .
Birth based caste system came through Manu smriti, which are temporary social laws and regulations for certain purposes in certain points in time. It was not meant to be permanent but became so due to force of tradition even though it contradicted the Shrutis or Vedas.
One becomes a Brahmana or Kshatriya through temperament or deeds and not by birth alone.
“Neither birth nor sacraments nor study nor ancestry can decide whether a person is twice-born (i.e., a Brahmin); character and conduct only can decide.” ~ Mahabharatha
"These were (originally) symbolic designations of the stages of spiritual refinement. They were not intended as social categories. And they were not intended to be hereditary. Things changed as the yugas [cycles of time] descended toward mental darkness. People in the higher castes wanted to make sure their children were accepted as members of their own caste. Thus, ego-identification caused them to freeze the ancient classifications into what is called the ‘caste system.’ Such was not the original intention. In obvious fact, however, the offspring of a Brahmin may be a Sudra by nature. And a peasant, sometimes, is a real saint.”- Paramahamsa Yogananda
One of the reasons for India's loss of sovereignty under foreign invasions and rule was the obsolete caste system which divided the Indian people and which prevented them from becoming a unified whole, even though the invaders were just a tiny fraction of the Indian population.
The invaders had superior social systems emphasizing equality and fraternity which made their small numbers formidable and superior.
An Indian professional soldier employed in the Indian army can be considered a Kshatriya. But even he would stake his claim to inheritance in a court of law . If he takes up arms and ammunition to fight taking Arjuna as an example, he will be reported to police who would put him behind bars, and he might even lose his job as well. The court will also take his violent disposition in society into account leading to higher chances of an unfavorable judgement against him.
