Small groups of families formed societies. The tribal chief or a King always desired to expand his power and have large empires. This desire of conquest was also for personal glory and was also encouraged by the people.
The advantages of a large empire under a King were as follows:
It created a sense of unity and brought people of different clans, with different customs and traditions together under a King.
A large empire also meant larger armies. Therefore, for an outside invader it was always a difficult task to go for a battle.
A large empire under one King unified the people and ensured all round development of the society, both economically as well as culturally.
Our scriptures talk of the Aswamedha Yagna and Rajasuya Yagna, wherein the emperor's horse was let loose to roam freely. Anyone who stopped the horse was duty bound to wage a war against the emperor. If it was allowed to roam freely all that land then the people were required to obey the laws, rules set by the emperor.
This was also a method to expand one's Kingdom. More importantly it was an idea of obtaining glory and distinction. The performance of the sacrifice, Asvamedha and Rajasuya, established supremacy of the ruler over a territory.
Dhanurveda and Nitiprakaska are ancient scriptures which describe in detail, the types and classification of weapons of war. Weapons were classified as per their use - those ones that are thrown (bow and arrow), those ones that are not thrown (sword) and those, which are used by mantra. Essentially, the sword, bow and arrow and the spear were the main weapons.
Our ancient scriptures describe in vivid details the making of a bow and arrow as well as the methods to use it correctly. The term Astra means a missile, which is thrown at the enemy. There were other weapons such as gada (long handle and a spherical head), parasu (battle axe), etc. Agneya Astra means a missile, which carries fire. The arrow of an Agneya Astra also called an Agni Bana consisted of a heated head or an arrow with fire on its tip. Such an arrow was more potent than a normal arrow.
Shukraniti (book on warfare by Shukracharya, an ancient guru) describes weapons of fire. Ancient Indians knew how to make an explosive and firearms were used extensively in battle. Ancient texts reveal that while gunpowder was known as 'Agnicurna', the guns were called 'Nalastra'. The 'Shukraniti' describes how gun powder can be prepared using saltpetre, sulphur and charcoal in different ratios for the use of different types of guns. Such a gunpowder was used to project missiles and rockets at the enemy.
Indian military science recognizes two kinds of warfare - the dharmayuddha and the Kutayuddha. Dharmayuddha is war carried on the principles of dharma, meaning here the Ksatradharma or the law of Kings and Warriors. In other words, it was a just and righteous war, which had the approval of society.
On the other hand, Kutayuddha was unrighteous war. It was a crafty fight carried on secretly. The Hindu science of warfare values both niti and shaurya i.e. ethical principles and valor. It was therefore realized that the waging war without any cause was not acceptable to the society.
A monarch desirous of dharma vijaya should conform to the code of ethics enjoined upon warriors. The principles regulating the two kinds of warfare are elaborately described in the Dharmasutras and Dharmasastras, the epics (Ramayana and Mahabharata), the Arthasastra (treatise of Kautilya), Kamandaka, and Sukra. Of particular interest was the rule that no army will destroy crops or houses of civilians. In fact the farmer and the general public were not affected by war and their lives were not disturbed. This ethos of the ancient army is practised by the Indian Army even today.
The ancient lawgivers, the reputed authors of "Dharmasutras" and "Dharmasastras" wrote the laws as per existing customs and usage for the betterment of mankind. The law books contain special sections on rules for the King and the warriors. A Kshatriya was required to perform three basic duties, learning, sacrificing and making gifts. The warrior was expected to learn all subjects that a King was taught.
They also learnt the art of "Dhanurveda". Much importance was attached to discipline and obedience. Even now a soldier is disciplined and obedient as a habit and virtue. The warrior was recognized by the dress he wore. The attire of a warrior was same for a Clear and each part of the dress was codified. He was expected to wear appropriate dress including jewels as per the occasion.
The warrior code enjoined that a soldier must die in the battlefield. Thus among the laws of war, we find that,
One of the laws enjoins the army to leave the fruit and flower gardens, temples and other places of public worship unharmed. The Ramayana describes how Ravana exhausted his arrows when fighting with Rama and Rama telling him to return the next day for battle with more arrows to fight. This incident was the highest form of Dharma yuddha practised.