"The Mission" 1986 film watch while it is available. It tells you why we go to war.

Sweeping and visually resplendent, The Mission is a powerful action epic about a man of the sword (Robert DeNiro) and a man of the cloth (Jeremy Irons) who unite to shield a South American Indian tribe from brutal subjugation by 18th-century colonial empires.  
We fight for God, country, and family so we say.

This storyline is written into our very human soul. This is our heritage as a species. It is how we made the world. I see no end in sight for the likes of humankind and this story explains why Rwandan genocide 800,000 April–July 1994 Hutu people vs. Tutsi Rebels Rwanda First Congo War 250,000–800,000 1996–1997 Zaire and allies vs. AFDL and allies Congo Second Congo War 2,500,000–5,400,000 1998–2003 See Second Congo War Central Africa War on Terror 272,000–1,260,000 2001–present Anti-Terrorist Forces vs. Terrorist groups Worldwide War in Afghanistan 47,000–62,000 2001–present see War in Afghanistan (2001–present) Afghanistan Iraq War 405,000–654,965 2003–2011 War in Darfur 300,000+ 2003–present SRF and allies vs. Sudan and allies vs. UNAMID Sudan Kivu Conflict 100,000+ 2004–present Congo War in North-West Pakistan 45,900–79,000 2004–2017 Pakistan, USA, and UK vs. Terrorist groups Pakistan Mexican Drug War 150,000–250,000 2006–present Mexico vs. Drug cartels Mexico Boko Haram insurgency 51,567+ 2009–present Multinational Joint Task Force vs. Boko Haram Nigeria Syrian Civil War 387,000–593,000+ 2011–present Syrian Arab Republic vs. Republic of Syria vs. ISIL vs. Syrian Democratic Forces Syria Iraqi Civil War (2014–2017) 195,000–200,000+ 2014–2017 Iraq and allies vs. ISIL Iraq Yemeni Civil War 233,000+ 2014–present Yemen’s Supreme Political Council vs. Hadi Government and Saudi-led Coalition Yemen Russo-Ukrainian War 40 000 – 100 000 2014 – Present Ukraine (and allied support) and Russia Europe Ethiopian civil conflict 300 000 – 500 000 2018 – Present Ethiopia, Eritrea, Sudan East Africa