According to some scriptures, in ancient times, Durga Navratri festival was a special festival for the Kshatriyas. The four-month long monsoon season was a critical time to perform any type of military activity. Hence, the Kshatriyas start their activities for new conquests. Kings worship Navadurga, nine manifestations of the Mother Goddess, before 9 days of beginning their army activities. The tenth day of the puja was considered as the day to begin their journey towards the battle field.
Durga or the Mother Goddess is the Goddess of War and courage as per Hinduism. As Kshatriyas or Kings give more preference to courage and war, Durga was considered as their Kul Devata. Ayudha Puja was one of the most celebrated events during Navaratri in ancient times of Kings and Kshatriyas. Kings perform Ayudha Puja on Durgashtami (eighth day) or on Mahanavami (ninth day) and moved forward to the battle field on Vijaya Dasami day.
In ancient times, during Durga Navarathri festival, animal acrifices were also performed to please Goddess Durga. Read here the Durga Navratri Vrat Katha or the story of Navaratri.
Here are the dates of Navratri 2017