A Kshatriya is a member of the military or reigning order, according to the law-code of Manu the second ranking caste of the Indian varna system of four castes, the first being the Brahmin or priestly caste, the third the Vaishya or mercantile caste and the lowest the Shudra.
Sanskrit kṣatriya is derived from kṣatra "dominion, power, government" and ultimately from a root kṣi "to rule, govern, possess".
In early Vedic civilization, the warrior caste was called rājanya rather than kṣatriya, an adjective to rājan "ruler, king" from a root rāj "to rule", cognate to Latin rex "king" and German Reich "empire".
In India, the period after the Epic Age or the Later Vedic Age (roughly 1000 BC to 600 BC) was marked by the rise of numerous small kingdoms. The rising popularity and aspirations of the Brahmin priests began to collide with the authority of the Kshatriyas, who formed the ruling class of each kingdom. The struggle involved the Kshatriya nobility and the Brahman clergy in all the Indo-Aryan regions from Iran to northern India.
The original Kshatriya families of ancient times in modern day are from the Khatri families of Punjab. In Punjab, the name khatri is the Punjabi dialect for the Sanskrit word Kshatriya. The Khatri, in modern day, is less of a land cultivator/agriculturalist, but more in a role as a businessman/merchant, civil & government administration, landlords, military officials, and as generals and soldiers. They are by far the most educated group in Punjab, along with the Punjabi Brahmins.
In modern India, caste is determined by familial inheritance, but not all present members of Kshatriya castes are necessarily descended from the Vedic Kshatriyas. Many historical rulers came from other castes, or were descended from non-Hindu foreign conquerers, and were either granted de facto Kshatriya status by virtue of the power they held, or they created fictionalized family histories to connect themselves to past Kshatriya rulers. The Maratha ruler Shivaji, for example, was from non-Kshatriya origins, but in order to legitimize himself as Maratha king he created a dubious genealogy that traced his family to the Sesodia dynasty of Rajputs, and found a prestigious Brahmin to conduct a ritual of consecration that aknowledged his kingship while absolving Shivaji of living as a non-Kshatriya. The caste system spread, along with Hinduism, throughout India and into southeast Asia, but not necessarily by immigration; peoples with non-Vedic origins may have adopted the vedic castes as they acculturated into Hinduism.
The Rajputs of Rajasthan and northern India claim to be the bona fide descendants of the Vedic Kshatriyas. The history of the Rajputs before c. 1000 CE is obscure, and historians have speculated on Rajput origins; some understand them to be relatively direct descendants of the Kshatriyas, while others favor a hybrid origin for the Rajputs, wherein Kshatriyas mixed with the descendants of invading warrior tribes from the northwest.
The Rajputs themselves usually do not take kindly to the hybrid theory: Traditionally, they view themselves as the only surviving pure Kshatriyas, claiming also that originally, this was the highest caste in the Hindu caste system, going back to an Indo-aryan patriarchal system of the king or dominant warrior at the apex of the social framework.
In addition to the Marathas, there are other Kshatriya communities in India, such as the Kunbis, Kurmis, Jats, Yadavs, etc. that were likely members of other agrarian or tribal communities, and were baptized as warriors by Hindu kings to supplement their armies.
See also: Hinduism, Varnas, Caste, Brahmin, Vaishya, Shudra,Untouchability, Aryan invasion theory