Some treaties and agreements allow countries’ commercial ships and planes to use certain of each others’ seaports and airports. Some cover commercial-aircraft safety standards and flyover rights; some protect property, such as foreign-owned investments, patents, trademarks, and copyrights. Countries also enact treaties for reciprocal reductions of import restrictions (remaining prepared, of course, to retaliate when another party interferes with trade flows by raising trade barriers or cutting diplomatic ties).