  Analyzing real data on international trade covering the time interval
1950-2000, we show that in each year over the analyzed period the network is a
typical representative of the ensemble of maximally random weighted networks,
whose directed connections (bilateral trade volumes) are only characterized by
the product of the trading countries' GDPs. It means that time evolution of
this network may be considered as a continuous sequence of equilibrium states,
i.e. quasi-static process. This, in turn, allows one to apply the linear
response theory to make (and also verify) simple predictions about the network.
In particular, we show that bilateral trade fulfills fluctuation-response
theorem, which states that the average relative change in import (export)
between two countries is a sum of relative changes in their GDPs. Yearly
changes in trade volumes prove that the theorem is valid.
