The document summarizes the development of the international laws of war, known as jus ad bellum, jus in bello, and jus post bellum. It describes how the Just War tradition originated in medieval Europe with theorists like Hugo Grotius, who was influenced by wars in Europe and sought to establish legal guidelines for justifiable wars. The basic ideas distinguish the circumstances under which going to war is acceptable, how wars should be conducted, and how they should be ended. These principles have influenced modern international law on the use of force.

1. THE INTERNATIONAL
LAWS OF WAR

2. The “Just War” tradition
was developed in
medieval Europe.
Its theorists were thinking
about this sort of war:

3. ...rather than this
sort of war:

4. In fact, its origins go
back as far as the
writings of some
ancient Greeks and
Romans.
This kind of war:

5. One of the most famous
theorists of “just war” was
this fellow -
Hugo Grotius.
He was a jurist from
Holland, born in 1583.

6. Grotius lived to see two
horrible wars - the Eighty
Years War between
Holland and Spain, and
the Thirty Years War
between Catholic and
Protestant nations in
Europe.
(This is a painting from the Thirty
Years’ War is called the Miseries of
War.)

7. This made him want to
write this book about war
and religion -
(“De jure belli ac pacis” means “On
the law of war and peace”)
The basic argument was
that some wars are
justifiable.

8. The idea of a just war
was heavily influenced
by the codes of chivalry -
Think knights in shining
armour, behaving
honourably, protecting
vulnerable damsels in
distress and so on...

9. The ideas about the justice of war are divided into three
parts:

10. 1.
jus ad bellum
ideas are about the circumstances under which it’s ok to
go to war

11. Jus ad bellum rules are
aimed at the people who
can make that decision -
heads of state.
Back when Hugo Grotius
was writing, that might
have meant this guy, King
Louis XIII of France,
known as “the Just”.

12. More recently, jus ad bellum
principles are speaking to
people like this chap:
George W Bush, was President of the
USA and “commander in chief” when
the US went to war against Iraq.

13. 2. Jus in bello ideas describe
the sort of behaviour that
is justifiable during a war

14. 3. Jus post bellum talks
about the proper way to
go about ending a war, for
example, in drawing up
peace treaties.

15. The principles of “Just War”
are not independently legal.
Still, they are fundamental
to the modern laws on the
use of force.
“Jus ad bellum” and “Jus in
bello” continue to be the
ways we categorise war law.
A famous example of “Jus in
bello” are the rules of the
Geneva Convention.

16. This course is about the legality of going to war - that is,
“jus ad bellum” law.

17. The way we - and our
military and civilian leaders,
and the lawyers who frame
our international laws -
think about war has
changed.
Crucially, after the horrors
of WWI, the western leaders
decided that war was, as a
rule, a bad idea.

18. So, in 1928, the Kellogg-
Briand Pact outlawed war.
It remains a binding treaty Not this guy:
for all the 63 states which
signed it into existence.
That’s this guy:

19. Clearly, the new law
didn’t quite work...

20. Sometimes, after all, needs
must.

21. Which is perhaps why, the
United Nations Charter...
(which is the effectively the
constitution of the UN, the main
guardian of international law in
the modern order)
...starts with a stern
prohibition against war...
and then provides
guidance on exceptions
under Article 51

22. This course is primarily interested in how going to
war can be ‘legal.’ What are the exceptions? Who
decides when they apply, and by what process?

23. Who knows, maybe this
course will help you pass
your exams...

24. Or it might just help you
sound clever at a
pretentious dinner
party...

25. In fact, that’s why we’re
gearing up to address a
question which you clever,
curious people have
probably thought about
and talked about before...

26. Was the invasion of Iraq in
2003 legal?

27. (As a special treat, those of
you who are that way
inclined can give us your
two cents on level 8)

28. Meantime... guess what?
You’re already one level
down!
Level 2, anyone?