Is a person breaking into your house an automatic threat on your life?

england-and-wales

No

There is a specific provision on householder cases under s76(5A) of the Criminal Justice and Immigration Act 2008:

In a householder case, the degree of force used by D is not to be regarded as having been reasonable in the circumstances as D believed them to be if it was grossly disproportionate in those circumstances.

The very existence of this provision makes it clear that when someone enters your house as an ostensible trespasser, self-defence does not automatically apply. If the court deems the use of self-defence to be grossly disproportionate under the circumstances, you may not have the right to use any form of self-defence (let alone "lethal force").

europe

In R (Collins) v Secretary of State for Justice [2016], it was confirmed that s76(5A) is compatible with the European Convention on Human Rights (ECHR). However, without the prohibition on lethal force in grossly disproportionate circumstances, this would have been found to violate the trespassers' Article 2 right to life.

Although R (Collins) is a judicial review in the UK, the subject matter concerns principles that apply to all parties to the ECHR. Therefore, with the exception of Russia and Belarus (as they are not parties to the ECHR), no country in Europe can provide a blanket allowance for the use of lethal force on a trespasser without being in violation of the Convention.

canada

In Canada, breaking and entering is not automatically treated as a threat to life.

For the purposes of self-defence, all the circumstances are considered in determining whether any action taken in self defence is reasonable. If would be an error of law if a judge allowed any single factor to control the analysis (or if they instructed the jury that this would be okay).

This comes from the text of the defence, codified at s. 34 of the Criminal Code. It reads:

34 (1) A person is not guilty of an offence if

(a) they believe on reasonable grounds that force is being used against them or another person or that a threat of force is being made against them or another person;

(b) the act that constitutes the offence is committed for the purpose of defending or protecting themselves or the other person from that use or threat of force; and

(c) the act committed is reasonable in the circumstances.

(2) In determining whether the act committed is reasonable in the circumstances, the court shall consider the relevant circumstances of the person, the other parties and the act, including, but not limited to, the following factors:

(a) the nature of the force or threat;

(b) the extent to which the use of force was imminent and whether there were other means available to respond to the potential use of force;

(c) the person’s role in the incident;

(d) whether any party to the incident used or threatened to use a weapon;

(e) the size, age, gender and physical capabilities of the parties to the incident;

(f) the nature, duration and history of any relationship between the parties to the incident, including any prior use or threat of force and the nature of that force or threat;

(f.1) any history of interaction or communication between the parties to the incident;

(g) the nature and proportionality of the person’s response to the use or threat of force; and

(h) whether the act committed was in response to a use or threat of force that the person knew was lawful.

I can imagine many scenarios where breaking and entering would not provide justification in Canadian law for the use of lethal force in response.

The law will not say so specifically, but in practice most states like Texas basically allow a homeowner to kill an intruder.

The Louisiana Stand Your Ground law (RS 14:19) will be extremely similar to Texas and similar states:

§19. Use of force or violence in defense

A.(1) The use of force or violence upon the person of another is justifiable under either of the following circumstances:

(a) When committed for the purpose of preventing a forcible offense against the person or a forcible offense or trespass against property in a person's lawful possession, provided that the force or violence used must be reasonable and apparently necessary to prevent such offense.

(b)(i) When committed by a person lawfully inside a dwelling, a place of business, or a motor vehicle as defined in R.S. 32:1(40) when the conflict began, against a person who is attempting to make an unlawful entry into the dwelling, place of business, or motor vehicle, or who has made an unlawful entry into the dwelling, place of business, or motor vehicle, and the person using the force or violence reasonably believes that the use of force or violence is necessary to prevent the entry or to compel the intruder to leave the dwelling, place of business, or motor vehicle.

This is an affirmative defense to murder or manslaughter charges. The problem in charging indiviuals is that the state of minds is decided by the defender. "Reasonably believes" is large enough to drive a semi-truck through. Louisiana has acquitted people who have shot people on their property, such as the Shooting of Yoshihiro Hattori. One can expect that an intruder in a home will have even less protection from the law. The way these laws are constructed makes it very difficult to prosecute. Beyond that, the typical political climate in such states means they are more likely to give the homeowner a medal than prosecute them.

No

new-south-wales

1. The law recognises the right of a person to act in self-defence from an attack or threatened attack.

2. It is for the Crown to eliminate it as an issue by proving beyond reasonable doubt that the accused’s act was not done in self-defence.

3. The Crown may do this by proving beyond reasonable doubt either:

   (a) the accused did not believe at the time of the act that it was necessary to do what they did in order to defend themselves; or

   (b) the accused’s act was not a reasonable response in the circumstances as they perceived them.

4. In determining the issue of whether the accused personally believed that their conduct was necessary for self-defence, the jury must consider the circumstances as the accused perceived them to be at the time.

5. If the jury is not satisfied beyond reasonable doubt that the accused did not personally believe that their conduct was necessary for self-defence, it must then decide whether the Crown has proved beyond reasonable doubt that the conduct of the accused was not a reasonable response to the circumstances as perceived by them. If the Crown fails to do so it will have failed to eliminate self-defence.

6. If the Crown fails to prove either numbers 3(a) or (b), it will have failed to eliminate self-defence. If it proves one or the other, it will have succeeded.

So, self-defence requires two things:

1. A subjective belief by the accused that their actions were necessary,
2. An objective assessment that the actions taken were what a reasonable person would do in the circumstances.

If the Crown can disprove either, it wasn’t self-defence.

The fact that the events took place during a break in of the accused home is one of the factors that make up the “circumstances”, but it is not the only factor. All else being equal, it seems likely that a break in may reinforce the accused’s belief in the necessity of their actions, and make more extreme action reasonable. However, these factors are not considered in isolation- the jury has to consider the totality of the circumstances.

Yes. I took a one hour law of force course in Texas.

Section 9.31 of Texas penal code says that use of force is presumed to be necessary if the target unlawfully and forcefully enters the actors habitation, vehicle, or place of employment.