Estate planning can become more complicated if you own assets outside of California or outside of the US. Among the considerations are the tax laws of those foreign jurisdictions, as well as the laws in those regions that may dictate how your assets are to be distributed after you pass away. For most, this is not a substantial problem to overcome, but it is important to be aware of the considerations.
Assets in other Jurisdictions
Other jurisdictions may not have the concept of a "trust" as we do here in California. Consequently, you may need to hire a lawyer in that particular country to understand how to appropriately plan your estate for property you may own in that country. Additionally, the laws in those countries may grant your family certain rights with respect to the property located in that country.
State Estate or Inheritance Taxes
California no longer has a "state estate tax", but other states still have such a tax. A "state estate tax" may also be referred to as an inheritance tax. Therefore, if you own property in states that have their own estate or inheritance tax, it's important to consult a lawyer in those states about how to plan appropriately.
International Tax Issues
It's important to remember that tax treatment between different countries can become even more complicated and may be affected by treaties put in place.
US tax laws are focused on making sure you are not avoiding taxes by shifting your property to other countries or by claiming property from other countries as gifts rather than income. Thus, even if you had a non-tax reason to move property to or from another country, it may have the unintended consequence of triggering tax laws.
If you own assets in multiple states and other countries, it's a good idea for you to consult with an estate planning lawyer to understand the potential issues you or your family may face.